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Chapter 3 — Affected Environment This chapter describes the biological, cultural, and on the eastern side of the valley floor, the Oligocene socioeconomic resources of the SLVCA that could be volcanic rocks of the San Juan Mountains dip gently affected by the no-action alternative (alternative A) eastward into the valley floor, where they are inter- and the proposed action (alternative B). The SLVCA bedded with valley-fill deposits. Valley-fill deposits consists of 5.2 million acres within the Southern Rock- consist of sedimentary rocks that inter-finger with ies and Arizona/New Mexico Plateau ecoregions (U.S. volcanic deposits. Quaternary deposits include pedi- Environmental Protection Agency 2011). The project ments along the mountain fronts, alluvium, and sand encompasses significant portions of seven counties in dunes (USFWS 2011). southern Colorado as well as small parts of two coun- ties in northern New Mexico. Just over 50 percent of MINERALS the total project area is publicly owned; however, the Sand and gravel are the major mineral commodities distribution of public/private ownership is uneven, with mined in the vicinity of the San Luis Valley. Rock, over 90 percent of Mineral County administered by sand, and gravel mines are scattered throughout the the USFS, but less than 1 percent of Costilla County valley, but are concentrated around the cities of Ala- in State or Federal ownership. The project boundary mosa and Monte Vista and the town of Del Norte, is defined by the headwaters hydrologic unit (HUC Colorado. No coal mining permits are active in the 6) of the Rio Grande. SLVCA (Colorado Division of Reclamation, Mining, Because of the nearly 7,000 feet in elevation change and Safety 2012). Other minerals that are mined in the across the project area, the SLVCA contains a diverse area include gold, silver, peat, and limestone. There array of plant communities, ranging from rabbitbrush is also nascent oil and gas exploration in the valley scrub and playa wetlands on the valley floor to alpine (USFWS 2011). tundra and scree fields on the peaks of the surround- ing mountains. As described in detail in this chapter, WATER AND HYDROLOGY the habitats of the valley and surrounding mountains Surface Water are crucial to the breeding and migration of migra- The SLVCA contains the upper headwaters of the Rio tory birds, and provide important opportunities for Grande watershed (Figure 2). Because of its position in persistence or reintroduction of populations of imper- a high-mountain desert, the valley floor receives little iled species that are protected under the Endangered precipitation, and most surface and ground water is a Species Act. result of runoff from the surrounding mountains. There are numerous perennial and intermittent drainages that descend from the Sangre de Cristo and San Juan Mountains. Some of the larger waterways include the Physical Environment Conejos, San Antonio, and Rio Grande rivers. A portion of the northern valley, known as the GEOLOGY Closed Basin or Sump, does not contribute water to The San Luis Valley is part of the much larger Rio the Rio Grande. The Closed Basin may have formed Grande Rift Zone, which extends from southern New in the middle Pleistocene when the lake that filled the Mexico northward through the San Luis and Upper valley began to dry up, resulting in an environment of Arkansas valleys to its northern termination near swamps and organic-rich sediments. Mayo et al. (2006; Leadville, Colorado (McCalpin 1996). The San Luis as cited in USFWS 2011) refer to the Closed Basin of Valley is bordered on the east by the linear Sangre Pleistocene time as the “ancestral sump.” Currently, de Cristo Mountains, which were created by exten- the Closed Basin covers approximately 2,940 square sive block faulting during the Laramide Orogeny. The miles in the northern part of the valley and is separated north-northwest portion of the valley is bordered by from the rest of the valley by a low alluvial fan. The the southernmost reach of the Sawatch Mountains. Closed Basin is composed of the San Luis and Sagua- The west side of the valley is flanked by the San Juan che creek drainage basins. Water enters the Closed Mountains, the result of extensive Tertiary-aged volca- Basin through precipitation and snowmelt from the nism. In sharp contrast to the steeply rising mountains 4,700 square miles of watershed in the surrounding 10 Draft EA, San Luis Valley Conservation Area, Colorado and New Mexico Figure 2 . The SLVCA captures the upper headwaters of the Rio Grande, the fourth longest river in the United States . Chapter 3 — Affected Environment 11 mountains. Water exits primarily through evapotrans- Grande on Alamosa NWR land. Salvaged Closed Ba- piration. Approximately 7,000 miles of stream chan- sin ground water helps Colorado meet its interstate nels and ditches flow through the valley. Surface water compact with New Mexico and Texas (USFWS 2012). flows into San Luis Creek, which flows generally to the south. There is no outlet, so water is impounded CLIMATE in San Luis Lake and associated lakes in an area south The climate of the San Luis Valley is consistent with of the Baca NWR (USFWS 2011). its high mountain desert setting, with substantial 24- hour temperature swings due to cold air drainage from Groundwater the surrounding mountains. This cold air also creates The project area is in the San Luis Valley portion of winter overnight temperatures that are often much the Rio Grande Aquifer System. The San Luis Valley lower than at many other places at similar elevations is the northernmost portion of the aquifer system that and latitudes. The mid-January high averages 340F stretches from Saguache County, Colorado, to West while the low averages -20F, and the mid-July high Texas (Robson and Banta 1995). The San Luis Valley averages 830F while the low averages 370F. is estimated to contain more than 2 billion acre-feet of Precipitation in the valley is strongly influenced ground water in storage, with more than 140 million by the surrounding mountains. The windward side of acre-feet estimated to be recoverable. The principal the mountain ranges, particularly the San Juan Moun- use of groundwater is agricultural (USFWS 2012). tains, receives a substantial amount of orographic The thick basin-fill deposits in the San Luis Valley precipitation, which is caused when air masses rise consist of interbedded clay, silt, sand, gravel, and vol- and subsequently cool, dumping their precipitation canic rock. These form many separate aquifer systems, at higher elevations. This results in a marked rain which are generally grouped into two major aquifers, shadow effect on the lee side of the mountains, with a shallow unconfined aquifer and a deep confined aqui- annual precipitation in Alamosa averaging 7.25 inches fer, though the lines between these features are not per year (National Weather Service 2012). absolute. Combined, these two aquifer systems are contained in valley-fill that can be as much as 30,000 feet thick (Brendle 2002). The unconfined aquifer is separated, but not totally disconnected, from the confined aquifer by clay layers and lava flows. The Biological Environment unconfined aquifer is recharged through infiltration of precipitation, irrigation water, runoff, and upward PLANT COMMUNITIES seepage of ground water from the confining bed. Dis- The vegetation across the project area varies greatly, charge from the unconfined aquifer is from ground depending on hydrology, slope, aspect, and elevation. water withdrawals, ground water flow to the south, See Figure 3 for an overview of general landcover. The discharge to streams or drains, and evapotranspira- San Luis Valley’s hydrology is strongly influenced by tion. Water levels in the unconfined aquifer respond the surface runoff and ground water flows from the to local climatic events and fall or rise with the avail- surrounding mountains. This hydrology has created a ability of precipitation. Wells drilled into the deep network of riparian corridors and wetlands that break confined aquifer are artesian and are buffered from up large expanses of associated desert and upland habi- climatic conditions. The confined aquifer is recharged tats across a 7,000-foot elevation gradient, resulting from precipitation and snowmelt in the high San Juan in high plant diversity. The six Colorado counties that Mountains and Sangre de Cristo Mountains. Discharge constitute the majority of the project area (Saguache, from the confined aquifer is from ground water with- Mineral, Rio Grande, Costilla, Conejos, and Alamosa) drawals, ground water flow to the south, and upward contain 1,132 species of plants (Appendix B; Colorado leakage through the confining bed (USFWS 2012). State University Herbarium 2012), which is more than A third aquifer system covers approximately 3,000 a third of the total plant species present in Colorado. square miles in the Closed Basin in the northern part Wetlands of the valley. This aquifer system has no natural sur- face water drain. The U.S. Bureau of Reclamation’s Wet Meadows . Wet meadow habitat is naturally pres- Closed Basin Project extracts ground water from ent in the San Luis Valley in areas that have shallow the sump. The water levels in the unconfined aquifer water tables and areas that are periodically shallowly in the Closed Basin are declining and ground water inundated early in the growing season. Wet meadows withdrawal is exceeding recharge (Rio Grande Water are the most widespread wetland type in the San Luis Conservation District 2012). Ground water from the Valley. Dominant plants include Baltic rush, hair grass, Closed Basin Project is carried in the Closed Basin and sedges. Most of the naturally occurring wet mead- Canal, which starts in the central San Luis Valley, ows have been modified by changes in water use, but passes south through Baca NWR, and ends at the Rio in some areas wet meadows have also expanded due 12 Draft EA, San Luis Valley Conservation Area, Colorado and New Mexico Figure 3 .

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