Cultural Resource Inventories and Climate Risk Assessment in California
Historical Geography Workshop: Mark HedlundUpdated: 4/24/2021
Abstract
Wildfires in California have destroyed several significant historic structures in recent years. Anthropogenic climate change will most likely increase the severity of wildfires and other climate events in the future. Predicting which buildings or cultural resources are vulnerable to climate events could direct preservation and mitigation efforts. Comparing the threats posed to historic resources by climate events to other causes could help us place the threat of climate change into perspective. A geographic inventory of cultural resources could be used to both understand the causes of resource destruction and assess resource vulnerability. Because California does not currently have a public geographic inventory of cultural resources, this study uses the National Register of Historic Places (NRHP) as a sample of an inventory. The strengths and weaknesses of using the NRHP as a sample are briefly explored. The causes of destruction of NRHP listed resources since 1966 is investigated. Overlaying spatial data of wildfire, flood, and sea level rise risk with NRHP resource locations highlights several resources and regions of concern. The results are available as a webmap and table of potentially impacted resources. The environmental review process for most large projects begins with determining an area of potential effect (APE). The APE is then surveyed; identified resources are evaluated; and adverse impacts are identified and mitigated. In conclusion, this study suggests treating the areas in California at risk of wildfire and inundation as if they were APEs in an environmental review project. Those areas should be surveyed, resources evaluated, and preservation efforts launched, before more climate related disasters strike.This paper was originally written for a class in the Johns Hopkins University AAP GIS master's program. It has been substantially re-written for this website. Although I am currently employed as a graduate student assistant at the California Office of Historic Preservation, this paper was written without any official assistance from, or coordination with, or endorsement by, that office.
The results of this study are available as a webmap here: Climate Threat to NRHP Resources Map
And in table form here: NRHP in California with climate risk
Introduction
Wildfires in California burned a record breaking 4,177,856 acres in 2020. Those fires killed 31 people and destroyed 10,488 structures. [1] Among the structures that burned were the majority of two National Register of Historic Places (NRHP) listed districts, part of a third, and at least one other NRHP listed building. Dozens of other listed properties narrowly escaped destruction. At least one National Register listed property was destroyed by wildfire in 2018. [2] While those fires were burning, I was employed as a graduate student assistant at the California Office of Historic Preservation. At that time there was no easy way to determine which historic structures were threatened by fire or which had been recently destroyed. Common knowledge of some historic buildings meant that threats to their safety were publicized in the media. It was widely reported, for example, when fires threatened or damaged historic wineries in Napa and Sonoma valleys. The fates of more remote and obscure structures went unreported and perhaps unnoticed. The fires in 2020 destroyed several wineries in Napa and Sonoma counties that were not listed on the NRHP but would have qualified for listing had they been nominated.
Anthropogenic climate change will likely increase the risk of wildfire and other extreme climate events in California. [3] How can we measure the risks that the changing climate will impose on our material cultural heritage? Can we measure the existing climate related risks to our historic structures and sites? This project is an exploration of those questions.
The National Park Service published a Cultural Resources Climate Change Strategy in 2016. This strategic framework offers broad direction and several actionable items for addressing climate risk to cultural resources. In the Science section, the value of geographic information systems (GIS) are mentioned several times. It is recommended that we assess resources for vulnerability to climate change and use “location to link existing descriptive databases and improve data consistency, quality and accuracy.” It is recommended that we monitor resources for the impacts of climate change. The NPS strategy recommends that we “integrate cultural resources into disaster preparation and response plans and practices.” In the Integrate Practice section we are reminded that one of the mandates of the National Historic Preservation Act (NHPA) is that we develop and maintain inventories of significant cultural resources. We can then use these inventories to assess resources for vulnerability and monitor the impacts of climate change. We can also use inventories and vulnerability assessments to plan for and mitigate impacts from anthropogenic climate change. [4] These suggestions are just part of a much larger needed framework for addressing climate change and cultural resources. Inventories and GIS are powerful tools though. This study hopefully helps illustrate their utility.
The value of preserving certain old buildings, structures, sites, or objects might not be self-evident to all. Historic preservation, as concerns buildings and similar material artifacts, is a culturally specific activity or preference. Some cultures place little or no value on preserving old buildings. Wahhabism and Modernism, as was practiced in mid-20th Century America, are two examples. This is not the place to argue the value of historic preservation, generally. It’s also not within the scope of this study to argue for the preservation of specific buildings or resources and not others. Many irreplaceable material resources in California such as intaglios and petroglyphs were created in the prehistoric period and are thus pre-historic resources. So, following the general practice, I adopt the term cultural resources for the subject of this study.
Cultural Resources Information Systems - Background
The energies of a large portion of the historic preservation community in the United States are focused on the threats to cultural resources posed by development or neglect. The threats posed by climatic events like wildfires and flooding have received less attention. This is at least partly due to the history of the preservation movement in this country. The historic preservation movement grew in influence in the 1960s as part of a reaction to overzealous urban renewal and freeway building campaigns. The legal structure we inherit from that reaction reflects the priorities of that period. [5] How do climate related threats to our resources compare to those posed by development or neglect? Does fire destroy more historic buildings than freeway construction? Does flooding destroy more buried prehistoric sites than looting? A solid answer to these and other related questions would require a study of a quantifiable resource population or a population sample. One of the questions for this study was; which resources will be inundated when the sea rises 10 feet, as it is predicted to rise? To answer that, we need to know the elevations and locations of a population of resources. The work to determine which areas of California are threatened by wildfire has already been done. To discover which resources are threatened by wildfire; we need to find the intersections between resource locations and wildfire risk locations.
Vast amounts of information concerning California’s cultural resources exists. Unfortunately, it is not organized in a way that facilitates creating baseline populations for study. Cultural resources information in California is fragmented and much of it is proprietary and or confidential. Most lists, registers, and databases of cultural resources in California are not maintained as live inventories. The California Register of Historic Places, California Historic Landmarks, Historic Points of Interest, and The National Register of Historic Places are all “list and forget” systems. Resources are not monitored nor are they necessarily removed from these inventories if they are destroyed. These systems work well enough if the main threat to resources is development, given that every new development will require a new survey and assessment. These systems work less well if we want to know how many historic structures were destroyed by wildfire in a specific year. The biggest challenge for this study was the fact that no statewide geographic inventory of cultural resources exists for California. If we knew the locations of all significant cultural properties, for example, we could use GIS software to quickly discover which resources were within a specific floodplain. This could indicate which resources were threatened by a coming storm. We could also quickly ascertain which resources were threatened by advancing wildfire lines and notify firefighting agencies of their existence. At this time, there is no mechanism for doing this in California.
The National Register of Historic Places as a Population Sample
When the National Historic Preservation Act (NHPA) was being drafted in the mid-1960s, the National Register of Historic Places (NRHP) was envisioned as a national inventory of significant historic structures and sites. [6] The NRHP in practice has several problems that make it a less than ideal inventory. But the NRHP has several advantages over other available alternatives. The California portion of the National Register contains a manageable 2,887 resources at this time (2/14/2021). [7] Each building, structure, site, or object in the NRHP is documented in a reasonably thorough way in nomination forms. Information about properties listed on the NRHP is in the public domain. Unfortunately, there was no reliably accurate, publicly available, geographic dataset of the NRHP. NRHP nominations contain location information though so it was possible to construct one for this study.
The NRHP was established in 1966 to be “the official list of the Nation's historic places worthy of preservation.”[8] The term “places” here is inclusive of buildings, structures, objects, sites, and districts. These are the bits of material culture that many historic preservationists have dedicated themselves to preserving. They are broadly referred to as cultural resources although in this sense the term “cultural resource” does not include small objects or works of art, immaterial things like songs, literature, memories, and other intangible resources.
The difference between a building or place that is “worthy” of preservation and one that isn’t is of course subjective. Cultural resource professionals (public historians, archeologists, architectural historians) have arrived at a kind of consensus around what constitutes a cultural resource and what kinds of things make those resources significant. The criteria for listing places on the National Register are one articulation of that consensus. Significance for NRHP eligibility is measured with four main criteria and then according to “integrity.” NRHP significance is always referential. It always comes from a connection to something else which is judged to be inherently significant. A resource can be significant because of its association with an event or movement (criteria A). A resource can be significant due to its association with a significant individual (criteria B). A resource can be significant because it is a good example of what is deemed to be high quality design or craft (criteria C). Lastly, a resource can be significant because it has yielded, “or may be likely to yield information important in prehistory or history.” This is typically interpreted to mean valuable to western scientific or academic interpretations of history and prehistory (Criteria D). [9] There are kinds of significance that are not included the NRHP criteria. They do not judge a building to be significant because it helps maintain a harmonious balance between old and new things, for example. Sites are not deemed significant when they possess the ability to teach us about our past or ourselves through visions or other means besides material evidence. Resources aren’t deemed to be significant because they serve as connections between ourselves and our ancestors. NRHP criteria are often argued and interpreted in flexible ways though which allows for the inclusion of a broad selection of resources. What is understood to be significant has changed over time and will keep changing. Some resources that were listed on the NRHP in the late 1960s and early 1970s might not be listed today. One of the biggest problems with studying climate effects on cultural resources will always be deciding which resources to focus on.
The process of listing a resource on the NRHP is involved and almost always requires assistance from a cultural resources professional. The mere fact that a resource is eligible for the register does not mean that it will be listed. The Golden Gate Bridge in San Francisco, for example, is not listed on the NRHP even though it is arguably one of the most culturally significant structures in the state of California. This is because no one has taken the time to document its history and context and argue its significance on a NRHP nomination form and then shepherd that nomination through the nomination process. As a result of the complexity of listing a resource on the NRHP, the register is a biased selection of properties. Each nomination reflects a specific motivation. Many resources are nominated to facilitate development. The Federal Historic Preservation tax credit is available for listed properties. [10] Many nominations are submitted to stop development. Groups opposing developments that involve demolitions of historic buildings have worked to get those buildings listed on the National Register as part of strategies to block development. This is a frequently unsuccessful tactic in that, while the buildings might be listed on the register, they are still demolished. Many nominations can be attributed to specific local avocational or professional historians who nominate buildings from their communities that they personally value. Some municipalities have programs or active historical societies that register local properties: other municipalities don’t. This causes wide differences in the number of registered properties between similar communities. Due partly to the cumbersome listing process, the National Register is far from complete. Around 60,000 resources in California have been determined to be potentially eligible or potentially eligible for listing on the NRHP by the State Historic Preservation Office. Yet at this time, less than 3,000 resources are actually listed. About 50 resources are added to the NRHP in California per year in recent years. The NRHP can be thought of then as a sample or selection of a larger population of cultural resources that could be listed on the NRHP at some point in the future.
Removing a resource from the register is almost as involved as having one listed. A simple call or email to the Keeper of the National Register to inform them that a building has burnt to the ground will have no effect on its listing status in the NRHP. The listing and removal processes are described in 36 C.F.R. Ch. I § 60.1 to § 60.15 (2012). [11] Dozens of structures continue to be listed in California decades after their destruction. The ways in which these structures met their fate is not recorded in the register nor is the date of their destruction.
Despite its problems, the NRHP appears to be the best source for a baseline cultural resource population sample in California at this time. Since 1966; 2,922 resources have been listed on the NRHP in California. Thirty-five resources have been subsequently removed leaving 2,887 listed resources as of 2/14/2021. As of 2021, 41 resources that are listed on the NRHP in California are known, to me, to have been destroyed. It’s unlikely that anything remains of a few dozen other resources but their status was impossible to confirm. For example, Big Gap Flume in Mariposa County or White's Gulch Arrastra in Siskiyou County have almost certainly disintegrated or been destroyed in fires. Are they still “worthy of preservation” then? That said, I estimate that at least 2,700 of the 2,887 listed resources still embody some of the qualities that justified their original listing. The NRHP inventory then has about 94% or higher accuracy.
Resources in the NRHP are classified as buildings, structures, sites, objects, or districts. Buildings are structures that can be used for human shelter whereas “structures” cannot be used as shelter. A house is a building. A dam, bridge or highway is a structure. A site is a location whose significance does not depend on a standing structure. Buried prehistoric material or the location of a significant event are “sites”. Objects are exterior works of art or design like monuments or fountains. Districts can be composed of any number of the former types of resources. Any resource that contributes to a district is effectively listed on the National Register. Some resources that are classified as buildings or structures have several contributing resources. Typically, if a single building, structure, site, or object is central to the significance of a resource and other contributors are secondary, the resource is not classified as a district. If there are two or more equally significant contributors to a resource then it is a district. [12] There are approximately 25,000 contributors to the 2,586 listed resources mapped for this study. Boats that have moved since their original listing were not mapped for this study (12). One operating locomotive, two buried ships, and any resource known to have been destroyed before 2018 were not included in this study or map. Nomination forms for 32 recently listed resources have not been published yet. Those were omitted from this study as well.
Tragically, looting and vandalism are still the biggest threats to many of the material cultural resources that are significant to California’s Native American population. Looted prehistoric artifacts continue to be bought and sold on sites like eBay with seeming impunity. The punishments for looting and destroying archeological sites on public land are light and perpetrators are rarely caught. For these and other reasons, the locations of prehistoric and historic period archeological sites are strictly confidential. There are 217 thus “restricted” National Register listed sites in California as of 2021. The fact that I cannot include those sites in this study is problematic. Archeological sites can be and are damaged by climate events.
NRHP Sample Distribution and Bias
The bias of the NRHP as a sample is important to consider. Using a sample of cultural resources that systematically fails to represent some cultures while over representing others is possibly unavoidable but efforts to compensate for and or understand that bias are warranted. The fact that Native American resources are entirely absent from this study is disappointing but there was no way I could include them at this time. Some bias is built into the four NRHP significance criteria. The other sources of NRHP bias are the multitude of different motivations held by the nominators of specific resources.
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As one might expect, the former houses of wealthy individuals seem to be over represented in the National Register. This is at least partly due to the influence of NRHP criteria B and C. Eligibility based on B is through association with a famous, often wealthy, individual. Eligibility based on C is often due to design by a well-known architect. Common homes in vernacular styles though are well represented in the NRHP. Hundreds of bungalow homes in Los Angeles County have been listed, for example. A wide variety of structure types are listed on the NRHP including: high voltage power lines, mining dredges, rocket launch pads, highways, trails, factories, ski huts, boats and docks, canals, a landfill and more. Buildings are by far the most numerous type of resource listed on the register. Of the 24,897 NRHP contributors to resources mapped for this study, 20,905 were buildings. Listed resources are highly clustered in urban areas, particularly in Los Angeles and the San Francisco Bay area. Los Angeles County has the most with 558 of the 2,586 resources mapped for this study. Los Angeles has 21.6% of the state’s listed resources versus 25.8% of the state’s population. San Francisco with 180 resources has the second most. Alpine, Glenn, Lake and Sutter counties have the least at just two resources each. Material cultural resources are records of human activity. Human populations constantly produce material culture and some of that material will rise to the level of significance that makes it worthy of preservation. One simple way to examine bias in the NRHP then is to compare listed resources with numbers of residents. Kings County has the fewest resources per person with 1 per 50,000 people. Sutter, San Bernardino, Kern and Madera all have fewer than 1 listed resource per 30,000 people. Sierra county has the most listed resources per capita with about 1 for every 300 people. Mariposa, Alpine and Modoc counties, which are also sparsely populated mountain counties have similarly high resource to resident ratios.
Cultural resources created by Native Americans in California have been excluded from this study. This is a substantial problem. Native Americans had been producing material culture in California for tens of thousands of years before European colonists arrived. Much still remains of what was produced and much of it is worthy of preservation. Native American cultures are still very much alive in California and continue to produce resources worthy of preservation. Hundreds of years of destruction and vandalism of Native American resources has required keeping their locations confidential. This means information about their locations can’t be published to a general audience. It also means that information about those resources is restricted by the state and federal governments to credentialed archeologists. There are 217 NRHP listed resources that are restricted in this manner in California. Almost all of the restricted resources in the NRHP are Native American resources. Those 217 restricted resources are almost the entirety of Native American cultures’ representation in the NRHP in California. In almost every case, those resources are judged to be significant according to NRHP criteria D which means they have value because of the information they might be able to contribute to prehistory or history. History here is understood to be the written records of Europeans and their descendants. Prehistory is almost always interpreted as being within the domain of archeological science which is a feature of European culture. Normally we know that the value of material cultural items is rooted in their connection and significance to the cultures that produced them. The practice of evaluating Native American material culture for significance has fallen into a pattern of disregarding the meaning and significance of objects and sites to the cultures that created them. Instead, all too often, we focus on what academically trained archeologists can learn from sites and material remains. This makes the NRHP evaluation process and criteria inadequate for judging the significance of cultural resources to Native Americans. NRHP criteria should not be the only framework used to determine which Native American resources are worthy of preservation. The California Native American Heritage Commission maintains the “Sacred Lands File” which is an inventory of resources and lands that are significant to California’s Native American tribes. [13] Access to that inventory is restricted. If that inventory exists as a spatial dataset then determining risk to those resources should be fairly simple. Ideally California would have a single inventory for native and non-native resources but this doesn’t seem possible at this time.
The legacy of systemic racism in California will result in the over representation of non-Hispanic white American culture in the National Register. Each listed resource owes its creation to one or more cultures. Identifying which cultures were responsible for each resource would require a significant amount of additional work. It’s easy however to compare contemporary socio-economic data to resource locations, once resources are mapped. This gives us some indication of the direction and amount of cultural bias in the NRHP in that it tells us who lives near, and sometimes in, properties the NRHP deems worthy of preservation.
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A general tendency for there to be more listed resources per capita in the northern part of the state than the southern can be seen in the maps above. It’s also true that the northern counties in California tend to have a higher percentage of non-Hispanic white residents than southern counties. The correlation softens a little in the third map where contributors per capita are shown instead of the number of primary resources.
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Some correlation between resources per capita and non-Hispanic white population can be seen in the graph above. Resources in the National Register can consist of a single structure like a house or over a thousand structures as in some districts. [14] The significant components of districts are said to be contributors. Comparing the number of contributors is perhaps more accurate than the number of resources since contributor counts add weight for the size of districts. Large historic districts with hundreds of contributing buildings might be more common in urban areas with more diverse populations. As can be seen below, when contributors per capita are compared to the percentage of non-Hispanic white population, the correlation is a little weaker. A better comparison would use a smaller and more consistent geographic unit than counties. Counties in California are a problematic geographic unit to work with since they vary so widely in both size and population. But smaller analysis units, like census tracts, would require mapping the locations of individual district contributors which would take many additional months of work.
Cultural bias in the NRHP exists and it can probably be measured. It is beyond the scope of this study to make further attempts to measure it, but we know it is there. It’s hard though to attribute the lack of listed resources in some counties to cultural bias. San Joaquin county, for example, has a close to average ethnic/race makeup for the state. It has a wealth of potentially eligible, but unlisted, structures in Stockton and elsewhere. San Joaquin county has one of the lowest ratios of listed resources to residents in the state. Lake county has no shortage of potentially eligible resources and has a higher percentage of non-Hispanic white population than most of the state, yet it has one of the lowest ratios of listed resources to population in the state. The agricultural central valleys and Imperial valley are generally underrepresented in the National Register. We must look beyond cultural bias to understand why this is. Lack of local interest in the NRHP program might be one reason. Lack of local interest in historic preservation, generally, might be partially responsible.
Vast swaths of urban America were demolished in the name of progress and slum clearance from the late 1940s to the 1970s. [15] Historic neighborhoods were deemed obsolete. [16] It was felt that urban transportation systems had to be adapted to the automobile with the construction of new freeways. [17] Countless irreplaceable historic structures were destroyed during those decades of urban “renewal.” The preservation law of 1966 (NHPA), the National Environmental Protection Act (NEPA) and the California Environmental Quality Act (CEQA) of 1970 were in part, reactions to the destructive, top-down approaches to urban and transportation planning that had been prevalent up to that time. Fifty years later it seems that those laws have been largely successful. Freeways are no longer built through vibrant neighborhoods, destroying them, as was the case in the 1950s and 1960s. Redevelopment agencies no longer demolish entire neighborhoods in the name of slum clearance. NHPA, NEPA and CEQA do not explicitly protect any resources though. Buildings and other resources that are listed on the NRHP are not explicitly protected from demolition. In fact, listed buildings are demolished regularly. NHPA, NEPA and CEQA established review processes that can slow projects and add costs to projects that threaten important cultural or biological resources. A core goal of NHPA and the preservation movement of the 1960s was to survey, evaluate and record resources in the paths of projects so that at the very least, we could know what was being threatened or destroyed. [6] In the years since 1966, hundreds of thousands of resources in California have been documented and evaluated in the course of development projects or agency inventories. Resources identified via projects with federal involvement are evaluated by the State Historic Preservation Office (SHPO) using the NRHP criteria. About 60,000 resources have been determined to be potentially eligible for the National Register by the California SHPO at this time. This is another view or sample of the same population of resources that the NRHP is drawn from. That population being the resources in California that are worthy of preservation. The resources determined eligible for the NRHP by the California SHPO are automatically added to the California Register of Historic Places. This much larger number of resources, 60,000, is, like the NRHP, a biased sample of a whole population. Resources that have never been in the area of potential effect (APE) of a federal project are likely to be missing from the California Register though they would qualify for listing. The California Register also contains resources that would not actually qualify for the NRHP because they were determined to be eligible with much less information available than is provided with a NRHP nomination. The exact size of the population that the California Register and the National Register are samples of, is unknown. Given the number of listed resources on the California Register, it could contain 60,000 or more resources. This would mean the NRHP in California is about 5% complete, if by complete we mean a comprehensive inventory of eligible resources. This is a lot of speculation. In any case, we know that the NRHP represents a larger population of similar resources. We can reasonably assume that that population is an order of magnitude, or more, larger than the 2,887 resources currently listed on the NRHP in California.
The Causes of Destruction of Listed Resources Since 1966
Using the NRHP as a sample can give us some idea of what kinds of processes destroy significant cultural resources in California. We can also use it to learn how those processes have changed over time. The NRHP is not a live inventory. Listed resources are not monitored. The causes of resource destruction are not tracked. It is a small enough sample though that manually tabulating listed and then destroyed resources is possible. Since the NRHP was established in 1966, 2,922 resources have been listed in California. In the intervening years, 35 of those resources were subsequently removed from the NRHP. There are many possible reasons for removal. The Hughes Flying Boat was removed from the NRHP in California because it was physically moved to Oregon. Five other resources were delisted because they were moved from their original settings thus losing the integrity of place. Those have been excluded from this study. Other removals from the NRHP were due to alterations, book keeping errors, or lack of clarity in the original nomination. After briefly researching each removal, I determined that 24 of those 35 delisted resources had been destroyed. An additional 41 resources have been destroyed but are still listed on the NRHP in California. The somewhat cumbersome process for removing a listed resource from the NRHP is outlined in 36 C.F.R. Ch. I § 60.15 (2012). [11] The information shown in the graphs below is the result of attempting to learn the fates of each of the 65 resources that were listed on the NRHP and subsequently destroyed. This includes cause and year of destruction. Well over a dozen additional listed resources are suspected to have been destroyed. These resources include remote cabins and other structures whose existence could not be verified via satellite imagery or other means. If positive confirmation of destruction couldn’t be found, resources were excluded from this study.
As can be seen in the graph above, the number of listed NHRP resources destroyed per decade peaked in the 1980s and has been lower since then.
In the graph above we can see the impact of the 1989 Loma Prieta Earthquake which destroyed several resources. We can also see that demolitions by both public and private developers have declined. Public developers include transportation and redevelopment agencies. This is a testament to the efficacy of NHPA, NEPA, and CEQA. We also see that wildfire had not been an identifiable cause of resource destruction before 2010. It’s probably not true that no resources were destroyed by wildfire before 2000, but none could be identified. Over all, private developers, municipalities, and accidental fires have destroyed the most resources.
The fact that almost as many NRHP listed resources have been destroyed in the first year of the 2020s as were destroyed in all of the 2000s and 2010s is alarming but there is no real reason to assume that this is the beginning of a trend. The decline in development related destruction does seem to be a trend. The rise in climate related destruction, specifically wildfire, is so recent that it might be an aberration. But wildfire severity is expected to increase with global climate change so this should be a concern. It’s interesting that other climate events like floods and landslides have not been known causes of listed resource destruction. Since the NRHP is a sample, the real number of resources destroyed by the above causes in recent decades is probably an order of magnitude or more, higher.
Resource Risk from Wildfire
Long dry seasons and hot summers make wildfire a fact of life in California. The risk of wildfire and the severity of wildfires is likely to increase in the coming years. In the last 20 years, wildfire has burned over a substantial part of the state as is shown in the map below. Not all fires are equal though and not all resources are affected by wildfires equally.
By overlaying the wildfire perimeters shown above with the locations of NRHP listed resources we can quickly discover which of those resources might have been impacted by recent fires. In the last two decades, 88 NRHP listed resources have had intersecting borders with published fire perimeters. These are shown highlighted in bright blue on the map below. Four of those 88 resources were destroyed completely including: The Honey Run Bridge, the Mountain House Historic District, and the Lower Sky Meadow Residential Area and Headquarters Building at Big Basin Redwoods State Park. The rest survived although some were damaged.
The wide variety of resource types in the NRHP makes determining the impacts of wildfire difficult. Many resources include a landscape component. If wildfire burns over a portion of the landscape, does it degrade the quality of the resource? Given that wildfire is a natural occurrence in California this is an important question. Some resources are inherently fire resistant. The Judson and Brown Ditch in San Bernardino County has been burned over by brush fires but probably not damaged, for example. In many cases fires have affected only small parts of larger districts. Small fires have broken out in Yosemite Valley, for example, without impacting the integrity of the larger district. Some resources however are highly combustible and can be thoroughly destroyed by fire. The wooden headquarters building at Big Basin Redwoods State Park, for example, was completely destroyed by fire in 2020. [18] There are also cases where seemingly vulnerable buildings have been entirely within the perimeters of wildfires and yet survived unharmed as was the case with the Pond Farm Pottery district in 2020.
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The map above shows the perimeters of wildfires in wine country in 2020 in red and NRHP resources in green. Nine NRHP listed resources are wholly or partially within wildfire perimeters in the map above. None of those resources were destroyed by those fires. Several of those resources were vulnerable wooden structures. This indicates that structures, even combustible ones, don’t have to perish in fires. Landscaping, fire hardening, local firefighting efforts and more can help structures survive wildfires. [19] The map above illustrates another aspect of wildfire which is that urban areas are safer but not completely safe from wildfires. St Helena and Calistoga were surrounded by fire in 2020. Both towns have multiple NRHP listed properties that would have been vulnerable had the fires reached them. Urban areas, even small ones, have advantages over rural areas in fire resistance. They have high pressure water systems for firefighting. They have abundant fire-retardant impermeable surfaces. They will be prioritized above other areas by firefighting agencies. But sometimes that’s not enough. The Tubbs fire swept through urban sections of Santa Rosa in 2017 destroying hundreds of homes and killing 22 people. Similar urbanized areas that are close to rural areas with high fire risk are common throughout the state.
The California Department of Forestry and Fire Protection (CAL FIRE) has made several spatial datasets that measure wildfire risk available to the public. The dataset I’ve chosen to use for this study was produced by CAL FIRE’s Fire Resource Assessment Program (FRAP). This data is distributed as a raster with 40-meter resolution. The fire threat raster combines “1) fire probability, or the likelihood of a given area burning, and 2) potential fire behavior (hazard). These two factors are combined to create 5 threat classes ranging from low to extreme.” [20] As can be seen in the map above, most of California has a moderate or higher threat from wildfire. The exceptions to this are the agricultural valleys and heavily urbanized areas. Because the production of material culture follows population, most NRHP listed resources are in urban areas and therefore don’t face much risk from wildfire. The types of accidental fires that destroy urban structures are typically not climate related and are a separate problem. Of the 2,589 resources mapped for this study, 633 are at least partially within one of the fire hazard zones that CAL FIRE has identified.
Some resources are not vulnerable to wildfire. The Malibu surf breaks are an example of a listed resource that won’t be damaged by fire because they are underwater in the ocean. The vulnerability of other resources like Thomas-Wright Battle Site, linear features like the Fages-De Anza Trail-Southern Emigrant Road, locations like Walker Pass, natural landscapes like Lower Klamath National Wildlife Refuge and resources like Barker Dam are debatable. Resource vulnerability to various kinds of destruction is not recorded or assessed as part of NRHP documentation. Vulnerability information could be valuable if it were recorded. The areas with the highest fire threat, extreme or very high, partially contain 136 listed resources. Larger resources like districts can cross multiple 40-meter cells in the fire threat raster. When those cells have different values they can be averaged to generate a mean fire threat score. There are 240 resources that have a moderate or higher mean wildfire threat score. Beyond this general sorting for potential wildfire threat, each resource needs to be considered individually. For example, Well No. 4, Pico Canyon Oil Field has the highest mean wildfire threat score in this study. It’s my understanding that most of the contributors, if not all, to that resource no longer exist, making preservation efforts pointless. The Davis Mill in Nevada County has a mean fire threat score of 4 or “Very High.” This resource, a wooden structure surrounded by heavy timber, appears to be highly vulnerable to wildfire. Each resource will have its own particular vulnerabilities or strengths in regards to fire. Active management and mitigation efforts can significantly reduce resource vulnerability.
There are a few noteworthy patterns in the map of fire threatened NRHP resources above. Large districts and long linear features are more likely to cross at least one area of fire risk. The long features that cross the southern San Joaquin Valley are high voltage power lines are contributors to the Big Creek Hydro-Electric Historic District. Some features of that district are highly vulnerable to fire. Some were probably damaged or destroyed in the Big Creek fire of 2020. The power-lines themselves however, might not be vulnerable. The large dairy landscapes/districts in Marin County, likewise, have varying degrees of risk and vulnerability. There are clusters of fire threatened resources in all of California’s National Parks. This is especially true of Yosemite and Sequoia and Kings Canyon national parks. The density of resources in parks is partly due to the fact that the National Park Service manages the NRHP program and is proactive about registering significant resources on land it manages. All federal agencies are required to create inventories of the cultural resources on their landholdings. [21] Some agencies do a better job of this than others. Registering the resources that satisfy the National Register criteria on the NRHP is an extension of the requirement to create inventories. The US Forest Service has a less active registration program than National Parks. This contributes to a noticeable falloff in resources just outside of National Park boundaries. Most of the land surrounding Yosemite and Sequoia/Kings National Parks is managed by the Forest Service. This suggests that there might be resources that are eligible for the NRHP but not listed in the areas surrounding those parks. Those resources would be similarly threatened by wildfire. Generally, there is substantial risk of wildfire throughout the Sierra Nevada and coast ranges. Those mountain ranges are home to several unique structure types and unique cultural landscapes.
The fire that destroyed the town of Paradise in 2018 also destroyed the NRHP listed Honey Run Covered Bridge. [2] That bridge was one of seven remaining 19th century covered bridges in California. The Glen Canyon Covered Bridge, formerly NRHP listed, was demolished in 1993. Covered bridges are a fairly rare structure type. They have many admirers who have published information about existing and former covered bridges in print and online. [22] All of those in California, built in the 19th century, have been listed on the National Register. As such, the National Register includes the entire population of 19th century covered bridges rather than just a sample. These bridges are made almost entirely of wood and are especially vulnerable to wildfire. The following six frame map compares the wildfire threat around five of California’s six surviving covered bridges. The sixth, not mapped, is the Wawona Covered Bridge in Yosemite National Park.
As can be seen above, all of these covered bridges are threatened to some extent by wildfire. The threat to the Oregon and Knights Ferry bridges is significantly higher than the others including the Honey Run bridge. The fact that the Honey Run Bridge burned and not one of the others is seemingly a matter random chance. The Wawona Covered Bridge, not shown above, is owned, and managed by the National Park Service and is surrounded by several other historic structures and park operations buildings. Presumably, it will receive extraordinary levels of fire protection. The Oregon and Bridgeport covered bridges are relatively isolated and might not. Having a comprehensive survey of a structure type allows us to know how close that type is to extinction. It allows us to compare risks to the surviving examples. It facilitates judging and comparing the qualities of the surviving examples. All of this could be useful for prioritizing preservation efforts.
The NRHP listed Davis Mill in Nevada County is one of 19 listed resources that have mean fire threat scores of “very high” or higher. The Davis Mill, which processed metal ores, is a traditionally constructed wooden building which is surrounded by forest. [23] It is thus very vulnerable to fire. The mill is an example of an important component of the mining landscape of the Sierra Nevada. That landscape is central to the history of California. To my knowledge, there have been no recent thematic surveys of the material resources associated with the mining landscapes of California. Mine mills and structures were once plentiful throughout the state but many have been destroyed by fire or deterioration. Several such mills are NRHP listed but, lacking a survey, we have no way of judging their rarity or risk of extinction. Lacking comprehensive surveys, we have no easy way of selecting the best surviving resources for preservation efforts. Thematic surveys could benefit and guide preservation efforts for many other types of resources in California. Structure types associated with agriculture, like hop kilns or early 20th century rice mills are not represented in the NRHP but probably should be. A thematic survey would help select the best examples of those resource types for inclusion in the NRHP.
The Threat of Inundation
Wildfire is an existing risk to cultural resources that is very likely to increase with anthropogenic climate change. Inundation is another existing risk that will increase in the coming years. Inundation from rising sea levels is almost certain to impact resources along the coast within a few decades. Inundation along streams and rivers from extreme precipitation events is also likely.
Coastal Flooding from Rising Sea Levels
Assessing risks to resources from sea level rise is fairly straightforward -- if there is an inventory of resources with known locations. The exact amount and timing of rising sea levels isn’t known. Estimates of the amount that mean sea level will rise by the year 2100 range from 2.5 meters to less than .25 meters. [24] I’ve chosen to use a 10 feet (3.048) meter mean sea level rise scenario for this study. This scenario was chosen largely because it was the highest estimate available in the spatial data NOAA has prepared as of 2020. Overlaying the predicted coastline after 10 feet of sea level rise with the locations of NRHP resources allows for the quick selection of potentially affected resources. There are 217 resources that would potentially be affected by 10 feet of sea level rise. Of that number, many are only partially affected. Larger resources such as the dairy districts in Marin county are affected only on their extreme edges. California’s coast is generally very steep. On most of the coast a 10-foot increase in sea level does not move the shoreline very far inland. The effects of coastal erosion are much harder to predict. Some resources, like lighthouses that are well over 10 feet above sea level, might be impacted by undermining, landslides and other processes related to erosion.
Many resources will be entirely inundated by rising sea levels. These are concentrated in bays and estuaries along the coast where the rise in land elevation is gradual. The most vulnerable resources are in urbanized areas that developed around ports and the mouths of rivers. Over half (131 of 217) of the resources threated by rising sea level are situated along the San Francisco Bay. Other concentrations are along Monterey Bay, in San Diego and the Los Angeles area. Most of the resources threatened by rising sea levels are embedded in urban landscapes that are likely to have many unlisted but eligible resources. Wave action is known to be highly destructive to buried archeological resources. Many irreplaceable buried prehistoric resources along the coast will be lost in the coming years. Surveys and inventories of coastal resources should be priorities for preservationists so that we can document what will be lost and prioritize preservation efforts.
Inland Flooding
Flooding from extreme precipitation events is a less certain risk than coastal flooding from rising sea levels. No NRHP listed resource has been destroyed by flooding in California since 1966, to my knowledge. Scottys Castle in Death Valley National Park was severely damaged in a 2015 flood though. [33] Floods have destroyed many listed resources in other states. A dozen listed structures were destroyed in the 1997 Red River flood in Grand Forks North Dakota, for example. Warmer temperatures globally will lead to more moisture in the atmosphere overall. California’s highly variable precipitation is likely to become even more variable as the global climate adjusts to warmer temperatures. [25] To see how much damage flooding from precipitation can do in California we can look at the flood in California in 1861-1862. If we faced those same conditions today, floods would likely destroy dozens or more irreplaceable cultural resources throughout the state. Predicting how soon a precipitation pattern like that of 1861-62, or worse, might happen is impossible. It is likely that we will face something like it again though, at some point in the future. [26]
I’ve chosen to use the National Flood Hazard Layer (NFHL) produced by FEMA for this study. The NFHL is designed to help asses flood insurance rates. [27] The NFHL spatial data FEMA distributes are complex. The goal of this study was to illustrate, in a very general way, the scope of flood risk to cultural resources in California. Doing this required summarizing and simplifying FEMA NFHL data in ways that probably reduce its accuracy and value. The Flood Hazard Areas layer is one of 30 component layers distributed with the NFHL. It covers most of California except for a few gaps. These flood hazard areas are coded using a two-part system, Flood Zone and Zone Subtype. I simplified the system into six seemingly logical groupings: floodplain, 100-year flood zone, 100-year shallow, 500-year flood zone, protected by levees, and minimal or no risk. A 100-year flood zone means there is a 1% chance of flood every year. In 500-year zones there is a .2% chance of damaging flood every year. These zones were then overlayed with the locations of NRHP listed resources. The most likely, highest risk zone, for each resource was then recorded in the resource’s attributes. Of the 2,589 resources mapped for this study, 721 have some exposure to flood risk. Many of those resources are only partially within flood risk zones. In some cases, the portions of resources that are in flood hazard zones do not contribute to the significance of the resource. Of those 721 resources, 89 were near the coast or a bay where water levels were dependent on sea level. Those resources were subtracted leaving 623 resources threated by precipitation related flooding. One hundred and five of those are protected by levees that satisfy FEMA’s standards. Scottys Castle is in an area of "minimal flood hazard" according to the NFHL.
This study does not consider buried archeological resources. Buried prehistoric sites can be, and are, destroyed by flooding. [28] Many of the 280 listed resources that are within floodplains or 100-year flood zones are vulnerable to flood damage. Other resources that are less likely to experience a damaging flood, those in 500-year flood zones for example, are nonetheless vulnerable to flood damage. These resources are widely distributed throughout the state. Humans tend to settle along waterways. Thus, our material culture accumulates along those waterways. Many of the waterways in California are susceptible to catastrophic flooding. Some areas that are at risk of destructive flooding are also probably underrepresented in the NRHP. Which is to say that those areas probably have a significant number of resources that are eligible for the NRHP but not yet listed. It seems that surveying areas at risk of catastrophic flooding and creating an inventory of significant resources in those areas should be a priority for preservationists.
Conclusions
The National Register of Historic Places is a selection drawn from a larger population of resources that are eligible for listing on the National Register. No one knows exactly how much larger that population is. That larger population is composed of all of the resources in California that are worthy of preservation. The process of listing resources on the National Register creates geographic and cultural biases in this selection. Despite its limitations, the National Register can be used to represent a larger group of resources that face climate related threats. The number of resources listed on the NRHP in California was small enough (2,887) that I was able to map most of them for this study. The National Park Service has published a spatial data representation of the National Register but that data was not accurate enough to be used in this study. [29] The California Register of Historic Places which includes about 60,000 resources is a much larger sample of the same or similar population as the NRHP. Creating a spatial dataset of the California Register would take years of work and unlimited access to unpublished state records. The California Historical Resources Information System (CHRIS) is not useful for this type of study because of its fragmented and proprietary nature. [30]
If we tracked the types of processes that destroy significant resources, we would have a better understanding of how to protect them. If we monitored resources in our inventories, we would have a clearer understanding of which resources still need protection, and which have already been destroyed. There are numerous national and state cultural resources inventory systems we can look to for ideas about how to improve ours in California. The English system, for example, has three tiers of significance. This allows for the listing of many more resources than a single, top tier, system like the NRHP. Anyone can nominate a resource to the English inventory by filling out a simple form. The research done to substantiate significance is then performed by professionals at the state funded Historic England organization. [31] A less arduous nomination process would hopefully reduce bias in the inventory. Imagine if anyone could submit a completed DPR 523 inventory form to the state office of historic preservation for concurrence the way federally funded developers do. The English inventory exists as an open access geographic data set. Anyone can download GIS data that describes the locations and some attributes of almost every one of the around 400,000 resources in Historic England’s inventory. [32] This would allow myself, or any interested person, to quickly determine which of England’s significant cultural resources are threatened by rising sea levels.
The three climatic threats examined in this study; wildfire, coastal flooding, and inland flooding, broadly affect three different types of landscape in California. As such they affect three different groupings of resource types. Wildfire threatens mountains throughout the state. Resources associated with the history of settlement by European and other immigrant groups in those areas are threatened by wildfire. Resources associated with the history of mining are threatened. There are many resources associated with the development of parks in the mountains that are threatened by wildfire. Coastal flooding from rising sea levels threatens the coastal landscape where the rise of the land is gradual. This includes ports and other low-lying parts of coastal urban areas. Resources associated with the development of ports and industry are threatened by rising sea levels. Resources associated with the military and coastal defense are threatened. Resources associated with the early urban development of California are threatened. Inland flooding potentially threatens landscapes along mountain streams and rivers and much of the agricultural valleys. Inland flooding threatens resources of all kinds throughout the state. About half, 1,229, of the 2,586 resources mapped for this study are potentially threatened by either wildfire or flooding.
Thematic surveys of resources associated with threatened landscapes could help determine which resources or areas to focus preservation efforts on. Thematic surveys can also help determine the absolute rarity of, or risk of extinction to, a resource type. Geographic surveys can be focused on areas with known risks. Surveys for cultural resources within 10 feet of mean sea level, for example, could tell us which resources will be lost in the coming years to rising sea levels. Surveys of areas at risk of wildfire could help identify vulnerable resources for conservation efforts. When NHPA and NEPA were enacted, one of the intentions was for resources in the path of development projects to be surveyed and documented before they could be destroyed. [6] We might think of rising sea levels, catastrophic wildfires, and extreme participation events as impending development projects. The areas of potential effect of these projects are known.
1. CAL FIRE: 2020 Fire Season, https://www.fire.ca.gov/incidents/2020/2. Honey Run Covered Bridge, https://hrcoveredbridge.org/
3. State Key Findings - California Climate Change Assessment, https://www.climateassessment.ca.gov/state/overview/#wildfire
4. NPS: Cultural Resources Climate Change Strategy, https://www.nps.gov/subjects/climatechange/culturalresourcesstrategy.htm, (2016)
5. Tyler, N., Tyler, I.R., Ligibel, T.: Historic preservation: an introduction to its history, principles, and practice. W.W. Norton & Company, New York (2018)
6. United States Conference of Mayors, United States, National Trust for Historic Preservation in the United States, United States Conference of Mayors eds: With heritage so rich. Preservation Books, Washington, D.C (1999)
7. NPS: Data Downloads - National Register of Historic Places (U.S. National Park Service), https://www.nps.gov/subjects/nationalregister/data-downloads.htm
8. National Register of Historic Places (U.S. National Park Service), https://www.nps.gov/subjects/nationalregister/index.htm
9. NPS: How to Apply the National Register Criteria for Evaluation, (1995)
10. Tax Incentives—Technical Preservation Services, National Park Service, https://www.nps.gov/tps/tax-incentives.htm
11. Code of Federal Regulations. (2012)
12. NPS: How to Complete the National Register Registration Form, (1997)
13. Forms – California Native American Heritage Commission, http://nahc.ca.gov/resources/forms/
14. View Park Historic District (U.S. National Park Service), https://www.nps.gov/places/view-park-historic-district.htm
15. Gordon, C.: Mapping decline: St. Louis and the fate of the American city. University of Pennsylvania Press, Philadelphia (2008)
16. Abramson, D.M.: Obsolescence: an architectural history. University of Chicago press, Chicago, Ill.; London (2017)
17. Teaford, J.C.: The rough road to renaissance: urban revitalization in America, 1940-1985. Johns Hopkins University Press, Baltimore (1990)
18. Chamings, A.: New photos show the extent of the destruction inside California’s oldest state park, https://www.sfgate.com/california-wildfires/article/New-photos-show-the-extent-of-the-destruction-15505442.php
19. Moore, H.E.: Protecting residences from wildfires: a guide for homeowners, lawmakers, and planners. U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, CA (1981)
20. CAL FIRE: FRAP GIS Data, https://frap.fire.ca.gov/mapping/gis-data/
21. Section 110--Federal Preservation Institute--National Park Service, https://www.nps.gov/fpi/section110.html
22. Adams, K.A.: Covered Bridges of the West: A History and Illustrated Guide: Washington, Oregon, California. Howell-North (1963)
23. Department of the Interior. National Park Service. (3/2/1934 - ): California SP Davis Mill. (2013)
24. Lindsey, R.: Climate Change: Global Sea Level, https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level
25. Huang, X., Stevenson, S., Hall, A.D.: Future Warming and Intensification of Precipitation Extremes: A “Double Whammy” Leading to Increasing Flood Risk in California. Geophys. Res. Lett. 47, (2020). https://doi.org/10.1029/2020GL088679
26. Swain, D.L., Langenbrunner, B., Neelin, J.D., Hall, A.: Increasing precipitation volatility in twenty-first-century California. Nature Clim Change. 8, 427–433 (2018). https://doi.org/10.1038/s41558-018-0140-y
27. FEMA: National Flood Hazard Layer | FEMA.gov, https://www.fema.gov/flood-maps/products-tools/national-flood-hazard-layer
28. Garrote, J., Díez-Herrero, A., Escudero, C., García, I.: A Framework Proposal for Regional-Scale Flood-Risk Assessment of Cultural Heritage Sites and Application to the Castile and León Region (Central Spain). Water. 12, 329 (2020). https://doi.org/10.3390/w12020329
29. NPS: National Register of Historic Places Map, https://www.nps.gov/maps/full.html?mapId=7ad17cc9-b808-4ff8-a2f9-a99909164466
30. About the CHRIS Information Centers, https://www.parks.ca.gov/
31. About Historic England | Historic England, http://historicengland.org.uk/about/
32. Download Listing Data - GIS Shapefiles | Historic England, http://historicengland.org.uk/listing/the-list/data-downloads/
33. NPS: Flash Floods of 2015 - Death Valley National Park (U.S. National Park Service), https://www.nps.gov/deva/learn/nature/flood-2015.htm
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