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Contemporary climate change is expected to affect the distributions of most species, but the nature, tempo, and mechanics of contemporary range shifts are still largely speculative. Here, we use fine-scale distributional records developed over the past Century, combined with spatially comprehensive microclimatic data, to demonstrate a dramatic shift in the range of a climate-sensitive mammal and to infer the increasingly important role of climate in local extinctions of this species across a 38.2 million-ha area. Changes in the distribution of the American pika (Ochotona princeps) throughout the Great Basin ecoregion were characterized using records from 1898-2008, revealing a nearly five-fold increase in the rate of local extinction and an 11-fold increase in the rate of upslope range retraction during the last ten years, compared with during the 20th Century. Four of ten local pika extinctions have occurred since 1999, and across this ecoregion the low-elevation range boundary for this species is now moving upslope at an average rate of about 145 m per decade. The rapid, ecoregional range shift of this small, talus-dwelling species stands in remarkable contrast with the dynamics and determinants of endangerment previously observed for most terrestrial species, and to earlier extinction determinants for O. princeps in this region. Further investigation of widely distributed species will clarify rates at which biotic response to environmental change is occurring, and how factors driving that change are evolving in different portions of the earth.