and aridic-f rigid moisture-temperature regimes (USDA Soil 

 Conservation Service 1978). The elevation ranges from ca. 5,300 

 feet near Dalys on the Beaverhead River to over 8,000 feet near 

 the Continental Divide. The climate of the basin is semi-arid 

 with warm summers and cold winters, becoming somewhat cooler and 

 wetter at the higher elevations in the foothills. Data from 

 nearby stations at Dillon (elevation 5,228 feet) and Lima 

 (elevation 6,265 feet) are taken to approximate the climate of 

 all but the highest elevations in the study area (from Geach 

 1972). Average annual precipitation was 11.34 inches in Dillon 

 and 9.92 inches in Lima with seasonal peaks in May and June. The 

 average monthly temperature in January was 22.8° F in Dillon and 

 16.3° F in Lima, and in July was 65.1° F in Dillon and 63.0° F 

 in Lima. 



Although extensive productive wetlands occur in Horse 

 Prairie Basin, these valley bottom sites are almost entirely 

 privately owned. Exceptions are the BLM holdings around the 

 inlets and outlet of Clark Canyon Reservoir, narrow riparian 

 zones along tributaries at higher elevations (e.g. Black Canyon 

 Creek, Bloody Dick Creek, Frying Pan Creek), and a few springs 

 and seeps. BLM lands are mostly in upland positions, where the 

 most common vegetation types are grasslands and sagebrush 

 grasslands. Lesser areas of coniferous forest occur at the 

 highest elevations and on northern aspects. The limestone 

 outcrops around Clark Canyon Reservoir are dominated by mountain 

 mahogany communities. 



The dominant land use in the study area is cattle grazing. 

 Most of the BLM land is in allotments to local ranches, and much 

 of this is heavily grazed. Forested BLM land on the western edge 

 of the study area has been utilized for commercial timber 

 harvest. Modern mining activity is mostly limited to gravel 

 pits, but historical gold placers are located along Jeff Davis 

 Creek, and other smaller prospects are scattered in the hills. 

 Recreation in the summer is concentrated around Clark Canyon 

 Reservoir, where fishing, power boating, water skiing, and 

 motorized camping are the most popular activities. In the fall, 

 the uplands throughout the basin are visited by large numbers of 

 hunters of antelope, deer, and elk (P. Hansen, pers. commun.). 



