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Plant macrofossils, percentage abundance of grass taxa, fecal-pellet δ¹³C, and plant-cuticle contents from 49 fossil rodent middens dated by ¹⁴C record changes in local vegetation and precipitation since 45 ka (calibrated or measured to thousands of calendar years before present) in the central Atacama Desert (lat 22°–24°S) of northern Chile. The midden sites are along the hyperarid upper margin (2400–3100 m) of the “absolute desert,” in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs. Conditions between 40 and 22 ka may have been at least intermittently dry, and possibly cooler, as implied by four middens with low species richness. We infer a large increase in summer rainfall between 16.2 and 10.5 ka on the basis of the lowering of steppe grasses by as much as 1000 m, prominence of C₄ grasses and summer annuals, high species richness, and displacement of …