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The historic distribution of pygmy rabbits (Brachylagus idahoensis) is discontinuous between the Great Basin and eastern Washington. Available data indicate disjunction may have occurred during the latest Pleistocene and earliest Holocene. Extralimital records indicate that the range of the pygmy rabbit decreased in eastern Washington during the last 3,000 years as the extent of sagebrush (Artemisia tridentata)-dominated steppe diminished. Relative abundances of pygmy rabbits and pocket gophers (Thomomys talpoides) in eastern Washington also appear to reflect responses to changes in the distribution and abundance of sagebrush.
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R. Lee Lyman (1991) studied this question.
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