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Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Inventory, Assessment, and Monitoring Programs

Sarah M. Lindley, Emily J. Wilkins, Carin Farley, Karla Rogers, Rudy Schuster, R.G. Sullivan · U.S. Geological Survey

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Land Management Research Program Prepared in cooperation with the Bureau of Land Management

Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Inventory, Assessment, and Monitoring Programs

Scientific Investigations Report 2024–5060

U.S. Department of the Interior U.S. Geological Survey

Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Inventory, Assessment, and Monitoring Programs By Sarah M. Lindley, Emily J. Wilkins, Carin Farley, Karla Rogers, and Rudy Schuster

Land Management Research Program Prepared in cooperation with the Bureau of Land Management

Scientific Investigations Report 2024–5060

U.S. Department of the Interior U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2024

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–392–8545. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/ or contact the store at 1–888–275–8747. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Lindley, S.M., Wilkins, E.J., Farley, C., Rogers, K., and Schuster, R., 2024, Delineating draft inventory analysis units for National Scenic and Historic Trails inventory, assessment, and monitoring programs: U.S. Geological Survey Scientific Investigations Report 2024–5060, 14 p., https://doi.org/10.3133/sir20245060. ISSN 2328-0328 (online)

iii

Acknowledgments The authors would like to thank internal reviewers Nicole Hill (U.S. Department of Agriculture Forest Service) and Brian Deaton (National Park Service). We would also like to thank all agency staff and contractors who took the time to talk to us about how they created inventory analysis units for prior inventories.

Contents Acknowledgments��iii Abstract��1 Background��1 Methods Used to Inform This Report��2 Current (as of 2024) Methods for Inventory Analysis Unit Delineation��3 Cross-Agency Comparison��3 Methods Used in Bureau of Land Management Inventory, Assessment, and Monitoring Reports to Delineate Inventory Analysis Units��4 Best Practices for Draft Inventory Analysis Unit Delineation��5 Viewshed Analysis for Draft Inventory Analysis Units��5 Viewshed Analysis Steps��7 Order of Operations��7 Example—Continental Divide National Scenic Trail in New Mexico��7 Conclusions��10 References Cited��10 Appendix 1. Inventory, Assessment, and Monitoring Procedure for National Scenic and Historic Trails��12 Appendix 2. Questions Used to Guide Group Discussion at the November 2023 IAM [Inventory, Assessment, and Monitoring] Evolution Meeting��14

Figures 1. Map showing a viewshed analysis for the Continental Divide National Scenic Trail in New Mexico and the resulting inventory analysis unit polygon drawn around the viewshed��8 2. Map showing draft inventory analysis unit constructed from the results of a viewshed analysis for the Continental Divide National Scenic Trail in New Mexico��9

Tables 1.

Summary table of inventory processes for the Bureau of Land Management, U.S. Department of Agriculture Forest Service, and National Park Service��4 2. Viewshed analysis parameter specifications from Bureau of Land Management inventory, assessment, and monitoring reports��5 3. Recommended parameter specifications for draft inventory analysis unit creation��6

Conversion Factors U.S. customary units to International System of Units

Multiply

To obtain

Length foot (ft)

0.3048

meter (m)

mile (mi)

1.609

kilometer (km)

Datum Horizontal coordinate information is referenced to the North American Datum of 1983.

Abbreviations BLM

Bureau of Land Management

CDNST

Continental Divide National Scenic Trail

DEM

digital elevation model

DSM

digital surface model

U.S. Department of Agriculture Forest Service

GIS

geographic information system

IAM

inventory, assessment, and monitoring

IAU

inventory analysis unit

NHT

National Historic Trail

NPS

National Park Service

NSHT

National Scenic and Historic Trail

NST

National Scenic Trail

Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Inventory, Assessment, and Monitoring Programs By Sarah M. Lindley,1 Emily J. Wilkins,1 Carin Farley,2 Karla Rogers,2 and Rudy Schuster1

Abstract

Background

As of 2024, there are 32 National Scenic and Historic Trails (NSHTs) in the system administered by the Bureau of Land Management (BLM), National Park Service, and U.S. Department of Agriculture Forest Service. The BLM administers, manages, and protects 19 of these trails as part of its system of national conservation lands. Various laws, regulations, and policies require that the BLM conduct and maintain an inventory to protect trail-related resources, qualities, values, associated settings, and primary use or uses. There are set procedures for conducting inventory, assessment, and monitoring (IAM) of NSHTs, as outlined in volumes 1 and 2 of BLM Technical Reference 6280-1. One of the first steps in the IAM process is deciding the area along a trail to inventory. However, volumes 1 and 2 of BLM Technical Reference 6280-1 do not specify how the land area to be inventoried should be delineated. The BLM calls these focus areas for IAM efforts “inventory analysis units” (IAUs), which are defined as the geospatial boundary for the location of an inventory along a trail. This report reviews the approach used to delineate the IAUs for an inventory effort and identifies best practices for creating initial IAUs, termed “draft IAUs.” Draft IAUs would provide standardization across multiple management jurisdictions by applying the same parameters for their delineation. These draft IAUs would provide trail managers with an area surrounding NSHTs that would trigger the need for an inventory if a project were proposed within it and are meant to be refined during localized inventory efforts. The best practices herein are for creating draft IAUs using standard parameters for performing a viewshed analysis to identify a proxy of land to include in an initial inventory effort.

The Bureau of Land Management (BLM) carries out a dual mandate through the Federal Land Policy and Management Act of 1976 (43 U.S.C. 1701 et seq.)—that of managing public land for multiple uses (for example, energy development, livestock grazing, mining, timber harvesting, and outdoor recreation) while conserving natural, historic, and cultural resources (for example, wilderness areas, dinosaur fossils, and national trails). The Federal Land Policy and Management Act of 1976 (43 U.S.C. 1701(a)(2)), the National Trails System Act of 1968 (16 U.S.C. 1241 et seq.), the National Historic Preservation Act of 1966 (16 U.S.C. 470 et seq.), and other laws, regulations, and policies require that the BLM conduct and maintain an inventory of trail-related resources, qualities, values, associated settings, and primary use or uses (BLM, 2012). The BLM's responsibility is to administer public lands “on the basis of multiple use and sustained yield”—except in areas specifically set aside for conservation purposes (BLM, undated a, p. 21). The BLM administers and manages more than 6,000 miles (mi) of 19 National Scenic and Historic Trails (NSHTs) in 15 States and more than 100 field offices (BLM, undated b). National Scenic Trails (NSTs) are more than 100 mi in length and are generally prohibited from motorized vehicle use. National Historic Trails (NHTs) are meant to commemorate historic travel routes of significance to the United States and may be designated for motor vehicle use (U.S. Department of Agriculture Forest Service [FS], 2014). Both NSTs and NHTs cross multiple jurisdictions, requiring extensive coordination with Federal, State, and local agencies; Tribes; and nonprofit partners. Because NSHTs cross multiple jurisdictions, there is an opportunity to compare agency inventory methods and policies, specifically with the National Park Service (NPS) and FS, to identify best practices and facilitate data sharing. The BLM has developed a standard approach for inventorying NSHTs that is described in volumes 1 and 2 of BLM Technical Reference 6280-1 (BLM, 2020a, b). The inventory, assessment, and monitoring (IAM) process for NSHTs requires inventorying for five different landscape

1U.S. Geological Survey. 2Bureau of Land Management.

2 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails elements: (1) scenic, (2) historic and cultural, (3) recreation (including recreational travel), (4) natural (including biological, geological, and scientific), and (5) other (such as night skies and lands with wilderness characteristics) (BLM, 2020a). The inventory of these landscape elements will depend on the defined nature and purposes of each NSHT because the inventory documents resources, qualities, and values that relate to the nature and purposes of each trail (BLM, 2020a). An IAM effort of NSHTs is triggered after trail designation, during the land-use planning process, or by a proposed action in the proximity of a NSHT (BLM, 2020a). When triggered, the NSHT inventory is initiated by an interdisciplinary team that consists of multidisciplinary trail specialists, resource specialists, and the trail administrator (BLM, 2020a). This effort often requires additional capacity from outside of the agency—such as contractors and partners—and trail associations, nonprofit partners, subject matter experts from other agencies, Indigenous communities, and local governments (BLM, 2020a). After initiating an inventory effort, the interdisciplinary team works to identify gaps in data, conduct the field inventory to fill data gaps, and assess the results. Refer to figure 1.1 in appendix 1 for a flowchart of the IAM process of NSHTs. Within the BLM, each office with trail responsibilities is required to conduct a trail inventory. Deciding the physical space to inventory is done in a four-step process (BLM, 2020b) as follows. 1.

Segment the trail based on condition, terrain, setting, and Federal protection components (in other words, highpotential historic sites and high-potential segments of NHTs). Inventory records are organized by trail segment.

Conduct a visibility analysis (herein referred to as a “viewshed analysis”), which acts as a means to identify the area of land around the trail to focus IAM efforts.

Delineate the inventory analysis unit (IAU) in relation to the viewshed.

Identify inventory points within the IAU. The IAU is a crucial component of the inventory process because it defines the area of land around the trail segment to focus IAM activities. An IAU is defined by the BLM as “a polygon encompassing discrete segments of the National Trail [sic] and the associated viewshed, based on the presence of similar conditions” (BLM, 2020a, p. 8). Based on the BLM’s IAM guidance, the process to delineate an IAU is to run a viewshed analysis from each respective trail segment and then use that viewshed to create a polygon. The resulting polygon is the IAU for the respective trail segment. However, in volume 1 of BLM Technical Reference 6280-1, there is no guidance on how the viewshed analysis should be conducted and what parameters should be used when running a viewshed analysis (BLM, 2020a). In volume 2 of BLM Technical Reference 6280-1, additional guidance is given specifically to monitor the scenic landscape element by placing points “at regularly spaced

intervals (typically 0.25 mile) along the National Trail [sic] segment” (BLM, 2020b, p. 3). Volume 2 of BLM Technical Reference 6280-1 also recommends that a 10-meter (m) digital elevation model (DEM) be used to run the analysis unless the interdisciplinary team geographic information system (GIS) specialist recommends a different resolution (BLM, 2020b). Other parameters for the viewshed, including the radius, are not specified in either document, and it is not clear how the interdisciplinary team should create the final IAU after the viewshed analysis. The parameters chosen for a viewshed analysis have the potential to significantly affect the geospatial results for what is visible on the landscape, which in turn has large implications for the area that is delineated for an IAU. To fill this gap and promote consistency, this report aims to better understand the processes and challenges of IAU delineation, and based on those findings, identify best practices for delineating IAUs in the future. For the rest of this report, we use the term “IAU” to refer to the space surrounding a trail for inventory purposes, except to mention and describe the terminology used by other agencies. As of 2024, large parts of NSHTs have not yet been inventoried; however, trail inventories are occurring as planning efforts or projects require. With IAM guidance requiring the identification of the IAU as part of an inventory effort, parts of trails that are not yet inventoried or prioritized for inventory could allow for unintentional and unknown loss of protection for resources, qualities, values, associated settings, and uses that are vital for the nature and purposes of the trail. Because NSHTs cross multiple jurisdictions, it is necessary to coordinate IAM as early as possible to meet the legal requirements. This report focuses only on the process for delineating IAUs, which is one component of the larger IAM process. For more information on conducting other aspects of the IAM process, refer to volumes 1 and 2 of BLM Technical Reference 6280-1 (BLM, 2020a, b).

Methods Used to Inform This Report This report was informed by (1) searching publicly available government documents regarding IAM of NSHTs to discern how they recommend IAUs be delineated, (2) reading IAM reports from the BLM and similar documents from the FS and NPS to determine how IAUs have been delineated on different NSHTs, and (3) having conversations with Federal staff and contractors involved with IAM of NSHTs to understand current (as of 2024) processes and challenges with IAU delineation. These three procedures are discussed in detail in the following paragraphs. First, we reviewed documents related to inventory efforts from the BLM, FS, and NPS. The BLM has IAM documents specific to NSHTs (BLM, 2020a, b), whereas the FS has documents describing inventory more broadly (FS, 1995, 2003), and we did not identify any related documents from the NPS. Within these inventory documents, we focused on any

Current (as of 2024) Methods for Inventory Analysis Unit Delineation 3 descriptions of how the land area around a trail is identified to be inventoried. After reviewing these documents, we had conversations with staff involved in trail administration at the FS and NPS to verify our understanding of methods for delineating IAUs for NSHTs. Secondly, we were aware of four inventory reports that have been completed about NSHTs since volumes 1 and 2 of BLM Technical Reference 6280-1 were published in 2020. These reports discuss the California (Applegate) NHT and Pacific Crest NST within Cascade-Siskiyou National Monument in Oregon (BLM, 2023a), the Continental Divide National Scenic Trail (CDNST) in New Mexico (BLM, 2023b), the Old Spanish NHT within Grand Staircase-Escalante National Monument in Utah (BLM, 2023c), and the Greenlink West Project involving multiple NHTs in Nevada (BLM, 2023d). We reviewed these reports specifically to identify how IAUs were delineated, including the parameters used for viewshed analyses. We also used these reports to help inform conversations with Federal staff and contractors about how certain decisions were made and parameters chosen for the IAU creation. In November 2023, the BLM hosted a 4-hour virtual IAM Evolution meeting with the goals of clarifying program guidance, improving and evolving IAM methods, informing database design, and creating programmatic efficiencies. This meeting involved 21 BLM staff and associated contractors who had a role in past or ongoing IAM efforts. In the morning, the BLM hosted a session specific to the inventory setup to better understand challenges and opportunities for IAU delineation and trail segmentation. This session used software that allowed participants to put virtual sticky notes on the screen color-coded to represent either opportunities and ideas or challenges and concerns. In the afternoon, there was a more in-depth discussion on IAU delineation and trail segmentation that focused on technical questions regarding methods used previously, staff perceptions of what could and could not be standardized, and staff recommendations for standardization (if any). The list of questions used to guide the afternoon discussion can be found in appendix 2. After the IAM Evolution meeting, we had two additional small-group discussions with specific meeting attendees who had additional perspectives to share. The questions used to guide discussions during these small-group meetings differed but focused on technical questions and questions specific to individual knowledge (for example, questions about individuals’ reports based on their involvement). All conversations with Federal staff and contractors—and the group discussion during the IAM Evolution meeting— were recorded and transcribed so we could refer to the conversations to ensure accuracy when needed.

Current (as of 2024) Methods for Inventory Analysis Unit Delineation Each of the three administering and managing agencies for NSHTs has its own processes for conducting inventories, whether documented in an official capacity or not. The following section examines the differences among these processes and the methods used in IAM reports.

Cross-Agency Comparison As mentioned in the “Background” section, the BLM’s approach for delineating IAUs for NSHTs begins with a viewshed analysis from the trail segment and then captures its outer perimeter to create a polygon. To learn more about best practices for developing viewsheds, we turned to Federal scenery management programs that often use viewsheds during inventory. Aside from the BLM’s guidance for inventory of NSHTs, the FS and NPS each possess their own national visual resource management programs with agency-specific manuals or documentation for conducting inventories (refer to table 1). As of 2024, the BLM is the only agency that has written operational guidance for inventorying NSHTs. Volumes 1 and 2 of BLM Technical Reference 6280-1 (BLM, 2020a, b) aim to develop a consistent and repeatable method for conducting an inventory of NSHTs—they create a standardized process for all national trails and can be used as a model for any agency attempting inventory efforts of NSHTs. At the time of this report (2024), only the BLM and FS have created reports regarding the inventory of NSHTs. The FS’ scenery management process is dictated by “Forest Service Manual 2300—Recreation, Wilderness, and Related Resource Management—Chapter 2380—Landscape Management” (FS, 2003) and “Landscape Aesthetics—A Handbook for Scenery Management” (FS, 1995), which comprise the FS’ scenery management system. The FS separates trail segments into units referred to as “scenic character units” that are grouped based on similar ecological factors. Overall, the FS follows the BLM guidelines laid out for the IAM of NSHTs. The NPS refers to “Documenting America’s Scenic Treasures—The National Park Service Visual Resource Inventory” (Sullivan and Meyer, 2016) for NSHT inventories, which uses the park unit as the designated area of importance and only requires inventory efforts when a development proposal occurs. This process is different from the BLM and FS given that the NPS is not a multiple-use agency. Trail administrators across the NPS, BLM, and FS may conduct a viewshed analysis related to individual National Environmental Policy Act of 1969 (42 U.S.C. 4321 et seq.) projects they are involved with to assist in determining the effects of proposed actions. These viewshed analyses differ in methodology given the different availability of NSHT data, DEM data, and preferences and analysis specifications chosen by the trail administrator.

4 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Table 1. Summary table of inventory processes for the Bureau of Land Management (BLM), U.S. Department of Agriculture Forest Service (FS), and National Park Service (NPS). [NSHT, National Scenic and Historic Trail; NA, not applicable]

Inventory Process

BLM1,2

FS3,4

NPS5

Are there published inventory reports specific to NSHTs?

Yes

Is there a documented plan or manual for conducting inventories on NSHTs?

Yes

How is space preliminarily created for an inventory?

Viewshed analysis

Already designated by park unit

What is the name of the space to inventory?

Inventory analysis unit

Scenic character unit

Park unit

When does inventory occur?

Proactively and reactively

Reactively

How does trail segmentation relate to unit designation?

One inventory unit per segment

Multiple inventory units per segment or multiple segments per inventory unit (dependent on scenic character unit)

Yes

If possible

Is there an on-the-ground component? 1BLM (2020a). 2BLM (2020b). 3FS (1995). 4FS (2003). 5Sullivan and Meyer (2016).

Methods Used in Bureau of Land Management Inventory, Assessment, and Monitoring Reports to Delineate Inventory Analysis Units A viewshed analysis uses a DEM to distinguish the land area that is visible from a specific point or set of points. For example, a person on top of a mountain would have a much larger viewshed than a person in a valley, and the exact extent to which a person can see can be determined from these DEMs. To conduct a viewshed analysis, specific parameters must be defined, such as the observer offset, surface offset, and radius. The observer offset (also referred to as “offset A”) is the height or level of the observer, whereas the surface offset (also referred to as “offset B”) is the height of the target being observed. The observer offset most often tends to be around the average eye level for adults (BLM, 2020b). The surface offset is usually set to 0 m (0 ft) to represent what someone could see on the surface of the Earth, but it can be set higher to analyze the effect of adding something to the landscape, such as a transmission line or wind turbine. The radius of a viewshed analysis is the chosen maximum distance that the viewshed is confined to. For example, a viewshed could span 10 mi, but if the radius was set to be smaller—for example, 5 mi—then the returned polygon for the viewshed would only span as many as 5 mi out from the trail. Staff and contractors from the BLM who were involved in prior inventories observed that there were parts of the IAU delineation process that were counterintuitive and would be difficult to generalize across locations. Specifically,

the trail segmentation required a level of inventory (field observation) to categorize the presence of high-potential route segments and similar trail conditions, trail characteristics, and ownership. Additionally, conversations with staff revealed that the process of segmenting a trail is highly localized and depends on the characteristics of each individual landscape; therefore, trail segmentation should occur once an inventory has started and the interdisciplinary team is assembled. Not having an initial IAU was troublesome for understanding the scope of the inventory effort. During the IAM Evolution meeting, staff from the BLM noted that refining the IAU after a viewshed analysis would be hard to accomplish without being physically present on the trail or having staff with on-the-ground experience. Therefore, the process for creating a final IAU should be flexible and allow for input and refinement by the interdisciplinary team. In 2023, four IAM reports involving NSHTs from the BLM were published with IAUs delineated using different viewshed specifications, which are shown in table 2. Conversations with BLM staff involved in these IAM processes revealed that the initial size of the radius in the viewshed analysis typically starts large (for example, 30 mi) and then is adjusted to the size that is the most intuitive for the landscape and area. For example, the size of the radius for Cascade-Siskiyou National Monument was 2 mi, whereas the size of the radius for the CDNST in New Mexico was 30 mi because the views are less obstructed. As shown in table 2, the parameters for the viewshed analysis differ across reports, and each of the reports uses a different radius. Of the two reports that specify offsets, different offsets were used as well.

Best Practices for Draft Inventory Analysis Unit Delineation 5 Table 2. Viewshed analysis parameter specifications from Bureau of Land Management (BLM) inventory, assessment, and monitoring reports. [NHT, National Historic Trail; NST, National Scenic Trail; km, kilometer; mi, mile; m, meter; ft, foot; CDNST, Continental Divide National Scenic Trail]

Location

Radius

Offset A (observer offset)

Offset B (surface offset)

Digital elevation model resolution

California (Applegate) NHT and Pacific Crest NST within Cascade-Siskiyou National Monument1

3.22 km (2 mi)

1.52 m (5 ft)

0.30 m (1 ft)

10 m (32.8 ft)

Clipped to Federal public land

CDNST in New Mexico2

48.28 km (30 mi)

Not specified

Only compared to groundlevel viewshed analysis

Old Spanish NHT within Grand Staircase-Escalante National Monument3

16.09 km (10 mi)

1.68 m (5.5 ft)

0 m (0 ft)

10 m (32.8 ft)

Clipped to the monument boundary

Greenlink West Project involving multiple NHTs in Nevada4

8.05 km (5 mi)

Not specified

Multiple used, not specified

Not specified

Viewshed from transmission lines and from trail

Notes

1BLM (2023a). 2BLM (2023b). 3BLM (2023c). 4BLM (2023d).

Best Practices for Draft Inventory Analysis Unit Delineation The current (as of 2024) BLM IAM guidance does not provide a technical description of how IAUs are to be developed, nor does it provide a technical description for how to perform the viewshed analyses that are used to identify the extent of land area to focus trail inventory. Therefore, the best practices in this section describe how to best fill in those gaps for a reproducible and consistent process for creating draft IAUs. Volume 1 of BLM Technical Reference 6280-1 describes that “the IAU should be broad enough to capture data about developments, facilities, and landscape or cultural modifications within the National Trail [sic] setting that may support or adversely impact National Trail [sic] resources, qualities, values, and associated settings and the primary use or uses of the trail” (BLM, 2020a, p. 20). These findings are the result of consultation with agency employees and partners involved in this work previously and the relevant literature. In this report, we recommend procedures for creating draft IAUs; however, before the final IAU is delineated, field staff should review the draft IAUs and adjust based on their local knowledge. Throughout this report, we use the term “draft IAU” to refer to the IAU that is created through standardized processes but before local refinement.

Viewshed Analysis for Draft Inventory Analysis Units The viewshed analysis parameter recommendations can be found in table 3. According to a visibility study of wind turbines in Wyoming and Colorado, the conservative suggested limit of the viewshed analysis radius is 30 mi (Sullivan and others, 2012). This research indicates that in optimal conditions, the human eye can see wind turbines as far as 36 mi away. However, a casual observer was only likely to notice turbines within 26 mi, indicating that 30 mi is a reasonable middle metric for visibility (Sullivan and others, 2012). Other studies noted similar visibility distances; for instance, a solar facility was visible from 29 mi when lit (Sullivan and Abplanalp, 2017), power towers were easily visible beyond 20 mi (Sullivan and others, 2013), and offshore wind turbines were visible beyond 26 mi (Sullivan and Abplanalp, 2013). These studies indicate that projects being proposed and developed, even if miles off a trail, have the potential to affect the nature and purposes of a NSHT and its Federal protection components. Additionally, conversations with BLM staff and partners indicated that 30 mi is a reasonable radius to use to create draft IAUs, with the understanding that the draft IAU would be refined to encompass only what is locally sufficient for monitoring and protecting the landscape elements that contribute to the nature and purpose of the trail. It is suggested that offset A, or the observer offset, be set at 1.52 m (5 feet [ft]) to account for the average eye-level height of adults in the United States (BLM, 2023a). This recommendation is consistent with volume 2 of BLM Technical Reference 6280-1. However, volume 2 of BLM Technical Reference 6280-1 does not provide guidance

6 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails on offset B (BLM, 2023c). Offset B, or the surface offset, should be set to 0 m (0 ft) because the draft IAU should be based on the person-level viewshed rather than any specific development or projects (which would have a higher offset). A DEM should be used as an input to the viewshed analysis rather than a digital surface model (DSM) because the DEM will result in a more conservative viewshed. A DSM consists of the elevation of the environment in addition to natural and built features of the landscape (for example, forest canopy, buildings), whereas a DEM only includes the environment elevation and so will assume more can be seen from the trail than a DSM. Volume 2 of BLM Technical Reference 6280-1 recommends using a 10-m DEM, and we concur with this recommendation because it balances a higher resolution result with the computation time necessary. However, a 10-m DEM will still have a large computation time if run over large spatial scales, so a lower resolution DEM may be necessary in the interest of computation time. The U.S. Geological Survey National Map Downloader (https://apps.nationalmap.gov/downloader/) maintains 10-m DEMs for the entire United States. When creating the polygon that encompasses the viewshed analysis to serve as the draft IAU, the Aggregate Polygon tool in ArcGIS (Esri, 2023) can be used to streamline and standardize this process. The recommended parameters for the Aggregate Polygon tool can also be found in table 3. Specifically, the aggregation distance, minimum area, and minimum hole size are set to 10 mi to mimic if the boundary were hand drawn around the viewshed analysis results, excluding no areas. The aggregate distance parameter specifies the maximum distance that polygons can be apart from one another and be combined. Minimum area and minimum hole size are the minimum sizes of polygons and polygon holes

to be retained. Using the Aggregate Polygon tool saves time when creating the polygons (compared to drawing by hand) and allows for increased consistency across all trails. For purposes of cross-jurisdictional coordination, resulting draft IAUs should not be edited to exclude any non-BLM lands, whether public or private (this same approach is used by the FS for viewshed analyses in scenic character units). The result of the viewshed analysis should remain as is, given that the viewshed does not differ depending on the land being public or private. Viewsheds should also not be limited by jurisdictional or State boundaries. When a trail involves partnerships with Canada or Mexico, it may be appropriate to allow the viewshed boundaries and draft IAUs to extend into those countries. As trail segments are inventoried for management, the draft IAU will be refined to a final IAU that consists of only the land area necessary to support the nature and purpose of each designated trail. This IAU will continue to be monitored and assessed according to policy. It is important to note for NHTs specifically that this viewshed only encapsulates what can be seen from the trail and that further efforts are needed to document associated heritage resources of NHTs. Notably, high-potential sites may be geographically separate from the designated alignment and therefore may be outside of the viewshed, which is another consideration for using a 30-mi radius to define the draft IAU. Even with that radius, there may be locations outside the perimeter of the draft IAU to include when finalizing the IAU because there may be elements that are important to the trail that are not within view from the trail. Further, draft IAUs do not represent a land allocation or special designation—they are informational in nature and intended to trigger an inventory and analysis for projects proposed within the boundaries.

Table 3. Recommended parameter specifications for draft inventory analysis unit creation. [km, kilometer; mi, mile; m, meter; ft, foot; km2, square kilometer; mi2, square mile]

Parameter

Recommendations

Viewshed analysis specifications Radius

48.28 km (30 mi)

Offset A (observer offset)

1.52 m (5 ft)

Offset B (surface offset)

0 m (0 ft)

Digital elevation model resolution

10 m (32.81 ft)

Polygon specifications Aggregation distance

16.09 km (10 mi)

Minimum area

25.90 km2 (10 mi2)

Minimum hole size

25.90 km2 (10 mi2)

Other

Not clipped to State boundaries or public lands

Best Practices for Draft Inventory Analysis Unit Delineation 7

Viewshed Analysis Steps The following steps describe the suggested method for how the viewshed analysis could be performed using ArcGIS Pro version 3.1.2 (Esri, 2023), although other GIS programs could be used to perform the viewshed analysis. An example of this procedure is provided in the “Example—Continental Divide National Scenic Trail in New Mexico” section of this report. 1.

Locate the official authoritative NSHT designated alignment GIS data from the trail administrator (file geodatabase, shapefile) and appropriate U.S. Geological Survey DEM rasters. The designated alignment should only be acquired from the trail administrator or partner who manages the designated alignment spatial data. This will ensure the alignment is correct and is the most up-to-date version.

Use the Generate Points Along Lines tool to create observer points every 0.25 mi according to volume 2 of BLM Technical Reference 6280-1 (BLM, 2020b).

Perform a viewshed analysis using the Geodesic Viewshed tool with the recommended parameters from table 3.

Transform the resulting raster from the viewshed analysis into a polygon using the Raster to Polygon tool.

Create a boundary around the viewshed using the Aggregate Polygon tool and recommended parameters from table 3, which will constitute the draft IAU.

Order of Operations Draft IAUs can be created on all NSHTs before inventories are conducted. A proposed project that intersects the draft IAU boundaries would trigger the need for an inventory of the trail resources before the managing agency can authorize the project. Once an inventory is triggered, the interdisciplinary team should segment the trails following the guidelines outlined in volumes 1 and 2 of BLM Technical Reference 6280-1 (BLM, 2020a, b). The refinement of the draft IAU would occur during the initial inventory effort based on fieldwork and understanding where the trail-related and contributing landscape elements exist. Although it is somewhat common in reporting of IAM efforts to include both the initial viewshed analysis and the resulting finalized IAUs, the process of moving from the initial allocation of space to the final IAU is not typically documented. Thus, these reports tend to leave a lot of steps unreported and are therefore not reproducible. Starting an inventory effort with a consistently delineated draft IAU introduces more transparency. Between the draft IAU delineation and refinement, the interdisciplinary team may decide to include an area beyond the original viewshed extent or exclude areas that do not contain anything significant to the

trail. For the greatest possible transparency in these processes, there should be an official documentation of the decisions that are made to refine the draft IAU to the final IAU and a description of the decision process. Refinement of the IAU will allow for the use of NHT heritage resource data that more accurately reflect the location of the NHT as compared to the designated alignment. Trail administrators and land managers must be in agreement regarding heritage resource data used in place of the designated alignment for analysis purposes. Participants in the BLM IAM Evolution meeting agreed that having draft IAUs completed for every NSHT was desirable. Generally, the perspective was that draft IAUs would be helpful in speeding up the inventory process. Specifically, this preplanning action would result in better IAM products compared to responding only to proposed actions. The draft IAUs would serve as a preliminary boundary inside of which a proposed action would result in a full IAM process. This creation of draft IAUs for every NSHT is the next step in the effort of documenting and inventorying trails.

Example—Continental Divide National Scenic Trail in New Mexico The recommendations described in table 3 are visualized by using the New Mexico portion of the CDNST as an example. The CDNST is a NST that consists of 3,100 mi between the borders of Alberta, Canada, and Chihuahua, Mexico. The CDNST follows the Continental Divide along the Rocky Mountains and crosses Montana, Idaho, Wyoming, Colorado, and New Mexico. Although most often used for hiking, the CDNST also is used by mountain bikers and horseback riders (Hill and Fothergill, 2022). Because the CDNST passes through 25 national forests, 21 wilderness areas, and 3 national parks, it is managed by the BLM, FS, and NPS (FS, undated). The CDNST is not one unbroken trail, and as of 2023, there are still gaps in the trail (Continental Divide Trail Coalition, undated). Figure 1 shows the CDNST in New Mexico and depicts the viewshed analysis results from using the parameters in table 3 and the resulting polygon that represents the draft IAU using the parameters in table 3 to delineate the polygon. Along with the best practices in this section for parameters, all areas that can be seen from the trail are included in the draft IAU. That is, there are no areas from the viewshed analysis excluded for any reason. Figure 2 shows the CDNST in New Mexico with the draft IAU created according to the best practices and steps discussed in this section. This example draft IAU would be used to inform the area surrounding the CDNST that would trigger an inventory if a proposal were within the designated area on the map. The final IAU would be edited after review from the interdisciplinary team during the localized IAM process.

8 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails 108° W

110° W

UTAH ARIZONA

106° W

104° W

COLORADO nJ MEXICO u aNEW n Riv Farmington er

CARSON NATIONAL FOREST

Riv er

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Gallup

n dia na Ca

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Colorado Plateau

ve r

Albuquerque

c Pe os

r ve Ri

CIBOLA NATIONAL FOREST 34° N

APACHE NATIONAL FOREST

Gil a

Roswell

White Sands Test Center

GILA NATIONAL FOREST

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r ve Ri ORGAN MOUNTAINS-DESERT PEAKS NATIONAL MONUMENT

Tucson

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UNITED STATES MEXICO

Carlsbad Las Cruces

El Paso

NEW MEXICO TEXAS

Ciudad Juárez

0 0

20 20

100 MILES

80 100 KILOMETERS

EXPLANATION

Continental Divide National Scenic Trail

KS OK

Map area

Draft inventory analysis unit Viewshed analysis

UNITED STATES TX MEXICO

Figure 1. A viewshed analysis for the Continental Divide National Scenic Trail in New Mexico and the resulting inventory analysis unit polygon drawn around the viewshed. The viewshed analysis and polygon were run using parameters outlined in table 3. Map created in ArcGIS (Esri, 2023).

Best Practices for Draft Inventory Analysis Unit Delineation 9 108° W

110° W

UTAH ARIZONA

106° W

104° W

COLORADO nJ MEXICO u aNEW n Riv Farmington er

CARSON NATIONAL FOREST

de Riv e

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d na Ca

SANTA FE NATIONAL FOREST

Colorado Plateau

ia n

SANTA FE

Ri ve r

Gr an

Gallup

Rio

Albuquerque

c Pe os

r ve Ri

CIBOLA NATIONAL FOREST 34° N

APACHE NATIONAL FOREST

Gil a

White Sands Test Center

GILA NATIONAL FOREST

Roswell

Sacramento Mountains

r ve Ri ORGAN MOUNTAINS-DESERT Las Cruces PEAKS NATIONAL MONUMENT

Tucson

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UNITED STATES MEXICO

CORONADO NATIONAL FOREST

El Paso

Carlsbad

NEW MEXICO TEXAS

Ciudad Juárez

0 0

20 20

100 MILES

80 100 KILOMETERS

EXPLANATION Draft inventory analysis unit from viewshed analysis Continental Divide National Scenic Trail

KS OK

Map area CA

UNITED STATES TX MEXICO

Figure 2. Draft inventory analysis unit (IAU) constructed from the results of a viewshed analysis for the Continental Divide National Scenic Trail in New Mexico. This figure shows that everything included within the polygon boundaries in figure 1 is part of the draft IAU. Map created in ArcGIS (Esri, 2023).

10 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails

Conclusions

References Cited

According to multiple legislative authorities, all National Scenic and Historic Trails (NSHTs) require an inventory of trail-related resources, qualities, values, associated settings, and primary use or uses—and that inventory is to be kept current. As of the time of this report (2024), there has not been an attempt to systematically delineate the geographic area that encompasses the potential resources that support the nature and purpose of each federally designated NSHT. Volumes 1 and 2 of Bureau of Land Management (BLM) Technical Reference 6280-1 provide guidance on how the inventory process is to take place, but they do not provide enough information on how to run viewshed analyses and delineate inventory analysis units (IAUs) in a systematic and repeatable way. The BLM guidance says to use a viewshed analysis for delineating IAUs, but it does not specify all the parameters used to run the viewshed analysis, or how to create an IAU from the viewshed analysis. Additionally, the four published (as of 2024) inventory, assessment, and monitoring (IAM) reports indicated each one was using different parameters for the viewshed analyses, resulting in IAUs of different sizes. This report provides guidance on the order of operations and parameters to be used for conducting a viewshed analysis to inform the development of draft IAUs and is based on conversations with staff who were involved in IAM, the available literature and IAM reports, and cross-agency comparisons of methods. Interdisciplinary teams can use these standardized draft IAUs as a consistent starting point for adjusting and delineating the final IAUs based on local experience, context, and inventory. Draft IAUs can be created on all NSHTs before inventories are conducted and would allow managing agencies to know when a proposed project may be within an area of a trail. Draft IAUs would be areas of special consideration that are meant to inform the public and managers of the existence of NSHTs that may be inversely affected by the proximity of proposed actions and require an inventory.

Bureau of Land Management [BLM], 2012, 6280— Management of National Scenic and Historic Trails and trails under study or recommended as suitable for congressional designation (P): Bureau of Land Management, [103] p., accessed January 22, 2024, at https://www.blm.gov/sites/blm. gov/files/uploads/mediacenter_blmpolicymanual6280.pdf. Bureau of Land Management [BLM], 2020a, National Scenic and Historic Trails inventory, assessment, and monitoring—Volume 1—Methodology: Washington, D.C., Bureau of Land Management Technical Reference 6280-1, 56 p., accessed January 22, 2024, at https://www.blm.gov/sites/default/files/documents/files/ Library_BLMTechnicalreference6280_01vol1.pdf. Bureau of Land Management [BLM], 2020b, National Scenic and Historic Trails inventory, assessment, and monitoring— Volume 2—Field guide: Washington, D.C., Bureau of Land Management Technical Reference 6280-1, 26 p., accessed January 22, 2024, at https://www.blm.gov/sites/default/files/ documents/files/Library_BLMTechnicalreference6280_ 01vol2.pdf. Bureau of Land Management [BLM], 2023a, CascadeSiskiyou National Monument inventory, assessment and monitoring report: Portland, Oreg., Bureau of Land Management, prepared by Logan Simpson, Fort Collins, Colo., 73 p. [Available from the Bureau of Land Management.] Bureau of Land Management [BLM], 2023b, Continental Divide National Scenic Trail Las Cruces District Office inventory, assessment, and monitoring report: Las Cruces, N. Mex., Bureau of Land Management, prepared by Logan Simpson, 170 p. [Available from the Bureau of Land Management.] Bureau of Land Management [BLM], 2023c, Grand StaircaseEscalante National Monument Old Spanish National Historic Trail: Kanab, Utah, Bureau of Land Management, prepared by Logan Simpson, 115 p. [Available from the Bureau of Land Management.] Bureau of Land Management [BLM], 2023d, National Historic Trails inventory and assessment report Greenlink West Project: Bureau of Land Management, prepared by Logan Simpson, Tempe, Ariz., 70 p. [Available from the Bureau of Land Management.] Bureau of Land Management [BLM], [undated] a, History of the BLM: Bureau of Land Management web page, accessed April 22, 2024, at https://www.blm.gov/about/history.

References Cited 11 Bureau of Land Management [BLM], [undated] b, National Scenic and Historic Trails: Bureau of Land Management web page, accessed April 2, 2024, at https://www.blm.gov/ programs/national-conservation-lands/national-scenic-and- historic-trails. Continental Divide Trail Coalition, [undated], Trail completion: Continental Divide Trail Coalition web page, accessed April 12, 2024, at https://continentaldividetrail.org/ trail-completion/.

U.S. Department of Agriculture Forest Service [FS], 1995, Landscape aesthetics—A handbook for scenery management: U.S. Department of Agriculture Forest Service Agricultural Handbook 701, [variously paged; 104 p.], accessed February 20, 2024, at https://www.nrc.gov/docs/ ML1224/ML12241A377.pdf.

Esri, 2023, ArcGIS Pro [version 3.1.2]: Esri software release, accessed February 20, 2024, at https://www.esri.com/en-us/ arcgis/products/arcgis-pro/overview.

U.S. Department of Agriculture Forest Service [FS], 2003, Forest Service manual 2300—Recreation, wilderness, and related resource management—Chapter 2380—Landscape management: Washington, D.C., U.S. Department of Agriculture Forest Service, 14 p., accessed February 20, 2024, at https://www.fs.usda.gov/about-agency/regulations- policies/manual/2380-landscape-management.

Hill, N., and Fothergill, D., 2022, Continental Divide National Scenic Trail scenic character descriptions: U.S. Department of Agriculture Forest Service, 176 p., accessed March 1, 2024, at https://www.fs.usda.gov/sites/default/files/CDT_ ScenicCharacterAssessment_Feb2022.pdf.

U.S. Department of Agriculture Forest Service [FS], 2014, National Scenic and Historic Trails program: U.S. Department of Agriculture Forest Service, 16 p., accessed February 20, 2024, at https://www.fs.usda.gov/Internet/ FSE_DOCUMENTS/stelprd3855600.pdf.

Sullivan, R., and Abplanalp, J., 2013, Utility-scale solar energy facility visual impact characterization and mitigation: Bureau of Land Management, prepared by Argonne National Laboratory, 53 p., accessed March 1, 2024, at https://blmwyomingvisual.anl.gov/docs/ SolarVisualCharacteristicsMitigation_Final.pdf.

U.S. Department of Agriculture Forest Service [FS], [undated], Working together—Land management agencies: U.S. Department of Agriculture Forest Service web page, accessed April 2, 2024, at https://www.fs.usda.gov/ managing-land/trails/cdt/working-together.

Sullivan, R., and Abplanalp, J., 2017, Visibility and visual characteristics of the Crescent Dunes solar energy power tower facility: Bureau of Land Management, prepared by Argonne National Laboratory, 94 p., accessed March 1, 2024, at https://blmwyomingvisual.anl.gov/docs/ CrescentDunesVisibilityReport_Final.pdf. Sullivan, R.G., Kirchler, L.B., Cothren, J., and Winters, S.L., 2013, Offshore wind turbine visibility and visual impact threshold distances: Environmental Practice, v. 15, no. 1, p. 33–49, accessed March 1, 2024, at https://doi.org/ 10.1017/S1466046612000464. Sullivan, R.G., Kirchler, L.B., Lahti, T., Roché, S., Beckman, K., Cantwell, B., and Richmond, P., [2012], Wind turbine visibility and visual impact threshold distances in western landscapes: Bureau of Land Management, prepared by Argonne National Laboratory, 47 p., accessed March 1, 2024, at https://blmwyomingvisual.anl.gov/docs/WindVITD.pdf. Sullivan, R.G., and Meyer, M., 2016, Documenting America's scenic treasures—The National Park Service visual resource inventory: National Park Service, prepared by Argonne National Laboratory, Denver, Colo., 26 p., accessed March 1, 2024, at https://blmwyomingvisual.anl.gov/docs/ SullivanMeyer_NPS_VRI_Final.pdf.

12 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails

Appendix 1. Inventory, Assessment, and Monitoring Procedure for National Scenic and Historic Trails The following is a graphic created by the Bureau of Land Management to outline the process for an inventory, assessment, and monitoring project. In addition, the graphic contains information about the staff involved in each step. Led by Trigger Trail designation, land use plan, trail comprehensive plan, or proposed action

Trail specialist Field office manager State program lead

Assemble inventory team

• Establish an interdisciplinary team • Identify the role of the trail partners and volunteers • Secure resources (funding, labor) • Execute memoranda of understanding/ intergovernmental agreements

ID team, which could include: trail associations; private/ volunteer partners; and subject matter experts from other agencies, Tribes, and local governments

Initiate an inventory effort

• Review the nature and purposes and management goals • Scope, schedule, and communication • Identify National Trail segments and baseline information and data gaps • Delineate inventory analysis units

ID team

Scenic

Conduct inventory

Historic and cultural Recreation Natural

• Document landscape element resources, values, associated settings, and primary use or uses

ID team Trail associations and private/volunteer partners Subject matter experts from other agencies

Add/Update records in corporate database

ID team Data managers

Other

Assess

• Evaluate how resources, values, associated settings, and primary use or uses support or detract from National Trail nature and purposes • Identify adverse effects or substantial interference

ID team Trail administrator

• Brief agency managers • Recommend Federal Protection Components, including high potential historic sites and segments to administrating agency • Incorporate into trail comprehensive plan and land use plan

Trail specialist Field office manager State program lead Adjacent State and National Trails managers Federal agency headquarters National Trails program lead Trail administrator Trail or site stewards

Monitor

Trail specialist ID team Trail or site stewards

Figure 1.1. The Bureau of Land Management’s (BLM) inventory, assessment, and monitoring methodology for National Scenic and Historic Trails (modified from volume 1 of BLM Technical Reference 6280-1 [BLM, 2020a, p. 7]). /, and (or); ID, interdisciplinary

Appendix 1. Inventory, Assessment, and Monitoring Procedure for National Scenic and Historic Trails 13

Reference Cited Bureau of Land Management [BLM], 2020a, National Scenic and Historic Trails inventory, assessment, and monitoring— Volume 1—Methodology: Washington, D.C., Bureau of Land Management Technical Reference 6280-1, 56 p., accessed January 22, 2024, at https://www.blm.gov/sites/default/files/documents/files/Library_BLMTechnicalreference6280_ 01vol1.pdf.

14 Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails

Appendix 2. Questions Used to Guide Group Discussion at the November 2023 IAM [Inventory, Assessment, and Monitoring] Evolution Meeting The following is a list of questions that we used to guide the afternoon group discussion regarding inventory analysis unit (IAU) delineation and trail segmentation at the November 2023 virtual IAM [inventory, assessment, and monitoring] Evolution meeting. The staff present at this meeting were those involved with IAM projects with the Bureau of Land Management.

Technical Questions and Trail Segmentation 1.

After action: How well did the IAU delineation process go? 1.1.

What are concerns? What would you do differently?

How did you handle overlapping polygons for multiple IAUs (for example., IAU for segment 1 overlaps with IAU for segment 2)?

How are decisions about segmentation of the trail made? For example, how do you decide on how many segments there are?

Would documenting how decisions are made for segmentation in the IAU products be helpful for decision support?

How do you decide on the specifications of the viewshed analysis (for example, offset and radius)?

Perceptions and Recommendations 6.

If we were to standardize the process of creating and refining IAUs, what recommendations would you have? 6.1.

What pieces would you recommend be standardized and what is context dependent?

How generalizable do you think the IAU process is? What pieces (if any) are highly context dependent?

Would each managing office drafting IAUs and (or) segmenting the trail before contracting help this process?

Would additional guidance on segmenting help the Bureau of Land Management?

Differences between National Scenic Trails and National Historic Trails 10.

What are the differences in the IAU specifications between scenic and historic trails?

11.

What recommendations do you have for developing IAUs for scenic compared to historic trails?

Publishing support provided by the Science Publishing Network, Denver Publishing Service Center For more information concerning the research in this report, contact the Director, USGS Fort Collins Science Center 2150 Centre Ave., Bldg. C Fort Collins, CO 80526-8118 (970) 226-9100 Or visit the Fort Collins Science Center website at: https://www.usgs.gov/centers/fort

Lindley and others—Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails—SIR 2024–5060

ISSN 2328-0328 (online) https://doi.org/10.3133/sir20245060

Delineating Draft Inventory Analysis Units for National Scenic and Historic Trails Inventory, Assessment, and Monitoring Programs

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