Located in south-central Idaho, the Snake River Basin Ecoregion spans 66,063 km2 (25,507 mi2) of mostly sagebrushsteppe (Artemisia tridentata) with some areas of saltbushgreasewood (Atriplex spp. and Sarcobatus spp.) and barren lava fields (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). The Snake River is the dominant hydrographic feature extending the full length (east to west) of the ecoregion. Elevation ranges from approximately 640 m in the “Treasure Valley” (Canyon County, near Nampa, Idaho) to 2,000 m in the semiarid foothills and eastern Snake River Plain. Mean annual precipitation ranges from 15 to 50 cm annually, and highest precipitation occurs in the high elevations of the dissected plateaus and Teton Basin along the eastern edge of the ecoregion. Mean January temperatures range from –14 to 4°C, with mean July temperatures ranging from 8 to 32°C.