ABSTRACr-Possible locations (189) of Washington ground squirrel colonies in Washington and Oregon were identified from the literature, state databases, museum collections, and converstions with local researchers and residents. In all, 80 confirmed and 7 probable colonies were found at 179 examined sites. Most colonies were small; the largest were on protected public lands. Squirrels were gone from 68 previously reported sites, and 25 additional sites were rated as highly vulnerable to extinction. Cultivation seems most responsible for range reduction. At 13 locations, 23 habitat variables were measured at 2 randomly chosen sites within a colony and also in a paired non-colony area. Although absolute values for some variables varied greatly between the 13 paired locations, Wilcoxon tests on the differences in the variables at each area showed that squirrels inhabited sites that had significantly greater grass and forb cover, deeper soil, weaker soil, and soil with less clay. These results suggest that food availability and soil characteristics are most important in determining where squirrel colonies are located within the habitats currently available to them. The Washington ground squirrel (Spermophilus washingtoni) is a little known rodent inhabiting the steppe grasslands of the Columbia Basin Province (Franklin and Dyrness 1988) in central Washington and northeastern Oregon. Although originally confused with the similar but unspotted Townsend's ground squirrel (Spermophilus townsendii) (Bailey 1936), its identification was clarified by Howell (1938) who described two subspecies on the basis of size. However, Dalquest (1948) found no size difference in specimens he collected and concluded that the subspecies were synonymous, and Hall and Kelson (1959) combined the two subspecific ranges of Howell (1938). Although he had no specimens from the more northern subspecies proposed by Howell (1938), Hill (1978), using numerical taxonomic and karyotypic methods, found no subspecific differences in populations separated by the Snake River. Other than general descriptions of its habitat, we know little of the natural history of S. washingtoni. Scheffer (1941) included comments on its food habits in a paper devoted mostly to S. townsendii and Dalquest (1948) claimed that burrows, nests, habits, and food of S. washingtoni are nearly identical to those of S. townsendii, as is hibernation as described by Svihla (1939).