DistributionRead full entry
Range DescriptionThis species is endemic to the west of the United States. Historically the range included much of the floor of the Central Valley (Sacramento and San Joaquin valleys) of California, from Butte County in the north to Kern County in the south, at elevations from near sea level to 122 m (Rossman et al. 1996, Ernst and Ernst 2003, Stebbins 2003). The species apparently is now extirpated from most of the range in the San Joaquin Valley (Rossman et al. 1996, USFWS 1993, Stebbins 2003). Extant populations are distributed in portions of the rice production zones of Sacramento, Sutter, Butte, Colusa, and Glenn counties; along the western border of the Yolo Bypass in Yolo County; and along the eastern fringes of the Sacramento-San Joaquin Delta from the Laguna Creek-Elk Grove region of central Sacramento county southward to the Stockton area of San Joaquin County (Hansen, cited by USFWS 1993). As of 1992, there were 13 known populations as follows (population = cluster of locality records in a contiguous habitat): (1) Butte Basin, (2) Colusa Basin, (3) Sutter Basin, (4) American Basin, (5) Yolo Basin-Willow Slough, (6) Yolo Basin-Liberty Farms, (7) Sacramento Basin, (8) Badger Creek-Willow Creek, (9) Caldoni Marsh, (10) East Stockton-Diverting Canal and Duck Creek, (11) North and South Grasslands (extirpated?), (12) Mendota (extirpated?), and (13) Burrell-Lanare (probably extirpated) (USFWS 1993). These population largely coincide with historical riverine flood basins and tributary streams. Populations 1 to 4 are associated with rice production zones; populations 5 to 13 mainly are in small, isolated patches of valley floor habitat.