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The Cascade Range in the northwestern U.S. acts as an orographic barrier to the easterly movement of humid air masses from the Pacific Ocean, producing a massive rain shadow with arid to semi-arid climate conditions on the leeward side of the range. Pedogenic carbonates formed in the C-3-dominated landscapes east of the range have delta C-13(carbonate) that is enriched by approximately 4 parts per thousand relative to carbonates formed in sub-tropical C-3-dominated ecosystems. We measured stable isotopic compositions of pedogenic carbonates preserved in the Quaternary and Neogene sedimentary rock units in the inland Pacific Northwest, and examined the impact of long-term aridification and paleohydrology on their isotopic compositions. The determined delta C-13(carbonate) record shows a gradual increase of 5 parts per thousand from approximately -10 parts per thousand in older pedogenic carbonates to -5 parts per thousand in younger ones whereas delta O-18(carbonate) record indicates a decrease of approximately 4 parts per thousand in the late Neogene. In addition, the Quaternary delta C-13(carbonate) and delta O-18(carbonate) records indicate the highest delta C-13 and delta O-18 among the samples during the Pleistocene and significant fluctuation over the time period. The gradual increase in the delta C-13(carbonate) ate and the decrease in the delta O-18(carbonate) in the late Neogene are interpreted by the development of the rain shadow as a result of topographic development of the Cascade Range. Changes in the Quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation, resulting from changes in large-scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet. The isotope record from pedogenic carbonates provides a direct record of climatic change, suggesting that long-term carbon isotope data can provide useful constraints on timing and intensity of regional desertification, and its associated climate and topographic interaction. (C) 2010 Elsevier B.V. All rights reserved.