Federal and Indian Lands on the U.S.-Mexico Border

The federal government owns roughly 640 million acres of land, about 28% of the 2.27 billion acres of land in the United States. In addition, the Bureau of Indian Affairs (BIA), in the Department of the Interior (DOI), is responsible for administering another 55 million acres held in trust for American Indians, Indian tribes, and Alaska Natives. Congress faces diverse issues pertaining to the management, development, and protection of federal and Indian lands.

Federal and Indian lands on the border between the United States and Mexico present unique challenges due to the remoteness and topography of the lands, length of the border, extent of federal and Indian lands, and differences in missions of managing agencies. These challenges are particularly at issue during congressional consideration of proposals to secure the nation's borders against terrorists and illegal entry of persons and goods, including through construction of fences and other barriers. Questions include how to facilitate access to these lands that allows for efforts to enhance border security while at the same time protecting natural and cultural resources and addressing environmental damage related to illegal cross-border activities.

This CRS In Focus provides an estimate of total linear miles of federal and Indian land on the southwestern border. It also identifies the portions of these lands managed by each federal agency in each of the four states along the border—Arizona, California, New Mexico, and Texas.

For an overview of federal land ownership, see CRS Report R42346, Federal Land Ownership: Overview and Data, by Carol Hardy Vincent, Laura A. Hanson, and Carla N. Argueta. For an overview of natural resource policy and management issues related to federal lands, see CRS Report R43429, Federal Lands and Related Resources: Overview and Selected Issues for the 117th Congress, coordinated by Katie Hoover.

Differing Estimates

There is no single, authoritative estimate of linear miles of federal and Indian lands on the U.S. border with Mexico. Instead, widely differing estimates have been reported in recent years, depending on the objectives established, sources consulted, and approaches used. Past estimates have included 632 miles (Government Accountability Office, or GAO), 648 miles (U.S. Geological Survey, or USGS), and 820 miles (DOI). For some of these estimates, there is insufficient information publicly available to determine how they were prepared and why they differ.

A variety of factors can affect federal land estimates and likely account for much of the variation in reported estimates of federal and Indian border mileage. One factor is the breadth of agencies reflected, specifically whether all or a subset of federal lands are captured. Similarly, some estimates might include Indian lands with the estimate of federal lands. Another factor is the source(s) used. Major geographic information system (GIS) sources of federal and Indian lands include the National Atlas, Protected Areas Database of the United States (PAD-US), and the U.S. Census (for Indian lands only). These sources reflect land ownership as of differing dates, and they vary in terms of precision and scale, among other variables. In addition, there are differing sources of GIS data from which the international border can be derived, and these sources can result in varying calculations of border length.

It is sometimes unclear from GIS sources whether federal or Indian lands are on the border or are located instead in close proximity to the border. In these cases, differing judgments could be made as to the inclusion of these areas. Further, some estimates may seek to capture only lands on the border whereas others might also seek to reflect lands in close proximity (e.g., within one mile of the border).

Variation in border mileage estimates also occurs based on the extent to which water features on the border are reflected in addition to land areas. Along the U.S.-Mexico border, federal areas that contain sizeable areas of water include two areas in Texas: Amistad National Recreation Area (National Park Service, or NPS), consisting of the U.S. portion of the International Amistad Reservoir, and the Lower Rio Grande Valley National Wildlife Refuge (Fish and Wildlife Service), located at the southern tip of Texas where the Rio Grande flows into the Gulf of Mexico.

CRS Estimate

Mileage

CRS estimates 693 miles of both federal and Indian land on the border, representing approximately 35% of the 1,965 miles on the southern international border. These lands are administered by a total of seven agencies.

Six of the seven agencies manage federal lands. They are the NPS, Bureau of Land Management (BLM), Fish and Wildlife Service (FWS), and Bureau of Reclamation (BOR), all in DOI; the Forest Service, in the Department of Agriculture; and the Department of Defense. The seventh agency, BIA, is the primary federal agency charged with carrying out the U.S. trust responsibility to American Indians, as noted, and thus Indian lands are reflected herein under "BIA."

These seven agencies manage differing amounts of land on the border, ranging from 10.1 miles for BOR to 195.1 miles for NPS. Of the four states, the most federally managed border mileage is in Arizona (298.5 miles) and the least is in California (61.0 miles). Table 1 contains the number of federal and Indian border miles by agency and state. Figure 1 portrays all federal and Indian lands on the border, and Figure 2 depicts these border lands by agency.

Sources and Methodology

The CRS estimate of 693 miles of federal and Indian lands on the border reflects lands managed by any federal agency as well as Indian trust lands under BIA. PAD-US was the primary source, because of the currency of the information (2016) and the detail as to ownership of small land parcels. U.S. Census Bureau data also were used for Indian lands and to identify the international border; these data reflect a total U.S.-Mexico border length of approximately 1,965 miles, as noted above. Further, to compare sources and methodology, CRS consulted with agency staff, including staff of the USGS and GAO who specialize in GIS data and take a lead role in federal government estimates of federal and Indian border lands.

The 693 miles is an estimate of federal and Indian lands with a boundary on the border as opposed to lands within a certain distance of the border. In some cases, it was difficult to determine whether federal or Indian lands shared a boundary with the border or were instead in very close proximity. CRS made these determinations based on a visual analysis of the GIS data, and other analysts could make different judgments.

With regard to water features, the estimate of 693 miles includes 94.2 miles within the Lower Rio Grande Valley National Wildlife Refuge and 36.4 miles of the Amistad National Recreation Area. However, the estimate does not include another 47.5 miles in Amistad consisting of waters that follow the international boundary (mid-channel in the Rio Grande), where there is no apparent adjacent dry land owned by the federal government.

Figure 1. Federal and Indian Border Lands	Figure 2. Federal and Indian Border Lands by Agency Sources (Figure 1 and Figure 2): CRS, using data from the Protected Areas Database of the United States, U.S. Census Bureau, and Esri 2016 Data and Maps.