4. Refuge Resources 4.1 Introduction Each of the two Refuges within the Sonny Bono Salton Sea NWRC protects very different habitats and species; therefore, this Chapter presents on overview of the regional setting, followed by separate descriptions of the various physical, biological, cultural, social, and economic resources within the Sonny Bono Salton Sea NWR and Coachella Valley NWR. 4.2 Regional Setting The Refuges of the Sonny Bono Salton Sea NWRC are located within the 8,360-square-mile Salton Basin (also referred to as the Salton Trough), a large natural depression that extends for almost 200 miles through the Colorado Desert (a portion of the larger Sonoran Desert) from a narrow point at the base of the San Gorgonio Pass in Riverside County trending southeast to the Gulf of California in Mexico (refer to Figure 1-1). The basin, which is the result of a deep, down-dropped fault block, occurs along the San Andres Fault at a point where two major tectonic plates, the North American Plate and the Pacific Plate, move past one another. The Salton Basin is flanked on the northeast by the San Bernardino Mountains and is within the rain shadow of the Peninsular Range, which borders the basin to the southwest. Most of the Colorado Desert lies at a relatively low elevation, below 1,000 feet, with the lowest point of the desert floor at approximately 275 feet below MSL. The summer daytime temperatures within the Colorado Desert are greater than the higher-elevation areas of the Sonoran Desert region and the occurrence of frost is extremely rare (CDFG 2007). Unlike the Mojave Desert to the north, which receives precipitation primarily during the winter months, the Colorado Desert, particularly the southern portion of the desert, generally experiences two rainy seasons per year, one in winter and another in late summer (CDFG 2007). The Salton Basin is included within the Colorado Desert region of California’s Wildlife Action Plan (Action Plan) (CDFG 2007). According to the Action Plan, the major stressors affecting wildlife and habitat within this region include water management conflicts and water transfer impacts; inappropriate off-road vehicle use; loss and degradation of dune habitats; disruption of sand transport processes; invasive plant species; and loss of habitat associated with growth and development. The Salton Sea and the Colorado River are identified by the Action Plan as the region’s two most significant aquatic systems. A few of the conservation actions proposed by the Action Plan to restore and conserve wildlife in this region include: 1) maintaining and restoring the Salton Sea ecosystem in a form that provides vitally important aquatic habitats; 2) protecting and restoring biologically significant habitats in the Coachella Valley through cooperative actions involving Federal, State, and local agencies and nongovernmental conservation organizations; and 3) securing resources, including funding for research, monitoring, and integrated pest management, from Federal, State, and local agencies to eradicate or control and limit introductions of invasive species in the region (CDFG 2007). The Salton Basin is also included within the boundaries of the Desert Landscape Conservation Cooperative (LCC), which encompasses portions of five U.S. states (i.e., Arizona, California, Nevada, New Mexico, Texas) and ten states in northern Mexico (i.e., Baja California, Sonora, Chihuahua, Sinaloa, Durango, Coahuila, Nuevo Leon, Zacatecas, Nayarit, San Luis Potosí, Aguascalientes). The U.S. Bureau of Reclamation and the Service are partnering to develop the Desert LCC, which represents a broad vision of conservation that includes working with partners ────────────────────────────────── Final Comprehensive Conservation Plan 4-1 Chapter 4 ───────────────────────────────────────────────────────── across landscapes to ensure that the necessary science capacity is in place to successfully address current and future conservation challenges (e.g., effects of long-term drought on the composition, abundance, and distribution of species; effect of reduced water availability on vegetation, wildlife, and human populations; changes in ecosystem productivity, structure, and composition resulting in changes in the rate of carbon sequestration and amount of carbon stored as biomass; changes in fire frequencies and intensities, due in part to the invasion of non-native grasses into native habitat areas). The Desert LCC will inform managers about potential impacts of climate change, develop adaptation strategies to assist in addressing these impacts, and provide a forum for on-going dialog between sciences and land managers. 4.3 Refuge Setting 4.3.1 Sonny Bono Salton Sea NWR Environmental Setting The Sonny Bono Salton Sea NWR is located in the southern portion of the Colorado Desert at the south end of the Salton Sea in Imperial County, California. As of 2010, the Refuge boundary encompasses approximately 32,410 acres of submerged land within the southern half of the Salton Sea and an additional 5,250 acres of upland and adjacent Salton Sea shoreline at the southeastern edge of the Sea (refer to Figure 1-2). Since 1995, the Salton Sea has been receding, resulting in approximately 700 acres of exposed playa on the Refuge. The Sonny Bono Salton Sea NWR is the only Refuge in the NWRS that is located entirely below sea level. The manageable portions of the Refuge consist of two areas, Unit 1, located near the southwestern end of the Salton Sea, and Unit 2, which includes the Refuge Complex headquarters, Union Tract, and Hazard Tract (Figure 4-1). Unit 2 is located approximately 18 miles to the northeast of Unit 1, at the southeastern end of the Salton Sea. The lands that abut the Refuge generally support agricultural uses; however, several properties in the general vicinity of the Refuge that previously supported agricultural uses are now geothermal production sites. Flyway Setting The Salton Sea is considered one of the most important habitats for birds in North America, supporting some of the highest levels of avian biodiversity in the southwestern U.S. (Shuford et al. 2002, Patten et al. 2003). The results of a yearlong study of the birds utilizing the Salton Sea (Shuford et al. 2002) documented the importance of the Salton Sea within the Pacific Flyway for A California brown pelican and brown booby squabble over wintering, migratory, and roosting rights (Mark Stewart/USFWS) breeding waterbirds. Various other studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. 4-2 Sonny Bono Salton Sea National Wildlife Refuge Complex ────────────────────── ─────────────────────────────────────────────────────────── ──────────────────── Refuge Resources Figure 4-1. Units of the Sonny Bono Salton Sea NWR ──────────────────────────────────────────────────────────────── Final Comprehensive Conservation Plan 4-3 Chapter 4 ───────────────────────────────────────────────────────── According to Shuford et al. (2002), in terms of overall shorebird numbers, the Salton Sea is the most important area in the Intermountain and Desert region of the West in spring and the second most important, after Great Salt Lake, in fall. Further, anecdotal evidence suggests there is a strong shorebird migrant connection with the west coast of Mexico, the Gulf of California, and the Pacific Coast of the U.S., particularly in spring. The Salton Sea is also strongly linked to the Gulf of California by northward post-breeding dispersal of species such as the brown pelican, wood stork (Mycteria americana), laughing gull (Larus atricilla), and yellow-footed gull (Larus livens). Historical Setting A combination of upland and wetland habitats occurred within the original boundary of the Refuge when it was established, but by 1941, the elevation of the Salton Sea was -242 feet MSL and rising, with the vast majority of the original Refuge submerged beneath the Sea. In 1945, an agreement was reached with IID to allow the Refuge to reclaim and improve lands within the area that today is referred to as Unit 1. Little of this area had been farmed and what portion was farmed had been fallow since 1924. As a result, major land alteration (e.g., land leveling, ditch and canal construction) was required before the land could be used to support forage crops for wintering waterfowl. By 1947, all of the original Refuge lands had been inundated and today this area is located under the southern end of the Salton Sea. To support waterfowl management and other uses, the IID in 1947 made available for leasing approximately 24,000 acres of upland that was situated between the southern edge of the Salton Sea and private farmlands. A portion of this area was leased by the Service for the Refuge. A number of the parcels located within the area of the Refuge referred today as Unit 2 were acquired through lease or purchase in the late 1940s and early 1950s. The lands within Unit 2 were already productive when the Service initiated its management activities; therefore, no major land alteration was necessary. By 1963, the elevation of the Salton Sea had risen to 231.65 feet below MSL, inundating all but about 4,415 acres of Units 1 and 2, and of that acreage, only 1,640 acres were suitable for uses that supported waterfowl and other waterbirds. Even the suitability of these lands was limited due to soil depletion and subbing (water movement in the soils) from the Salton Sea. Because of the lack of adequate farmland to raise cereal grain and green forage foods for waterfowl, impoundments were created in 1962 to produce alkali bulrush to supplement foraging opportunities for waterfowl. The ongoing management of these refuge lands is described further in Chapter 3. 4.3.2 Coachella Valley NWR Environmental Setting The 3,709-acre Coachella Valley NWR is located near the center of the Coachella Valley, to the northeast of Palm Desert, in an unincorporated portion of west-central Riverside County, California (Figure 4-2). Riverside County covers over 4.7 million acres (7,310 square miles), making it California’s fourth largest county (CVAG 2007b).