The Patagonian Desert, like other rain shadow deserts around the world, lies adjacent to a mountain range, which physically lifts oncoming westerly winds laden with moisture. As the range became higher, the amount of water remaining in weather systems that were able to cross the topographic barrier became smaller. The height of the range is also reflected in the degree of Rayleigh fractionation of stable hydrogen and oxygen isotopes in rising water vapor. The isotopic composition of precipitation from these vapor masses can be recorded in leaf wax molecules and carbonate nodules, both of which are preserved in paleosols. I will sample leaf waxes from a previously described and dated Miocene section and then interpret them in light of data from previously measured carbonate nodules as well as the modeled relationship between precipitation chemistry and the elevation of the crest of a mountain range. The results of this work will allow me to answer two questions: 1) when did the Patagonian Andes rise, placing a rain shadow across the once-humid climate of Patagonia, and 2) do plants and soil carbonates record the same isotopic composition of precipitation? Both questions pose testable hypotheses that can be clearly answered using stable isotope data from paleosols. The results will substantially enhance our understanding of regional Cenozoic paleoclimate and inform thinking on the linkages between terrestrial paleoclimate and paleoelevation.