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The stable isotope ratios of meteoric waters change predictably over orographic barriers. We present a new approach to determine stable isotope ratios in ancient meteoric waters from spatial patterns of hydrothermal alteration in continental volcanic fields. In the San Juan Volcanic Field, Colorado, USA we reconstruct water δ18O values feeding hydrothermal systems of −7 to −10‰ from 35 to 20 Ma, followed by a drop to −17 to −18‰ between 20 and 12 Ma. This drop is consistent with greater magmatic water input to older hydrothermal systems, ∼1 km of rock exhumation, ∼2–3 km of surface uplift, or a combination of all three. Our approach returns water isotope compositions integrated over spatial (kms to 10s kms) and temporal (104 − 107 years) scales of continental hydrothermal systems. Such length‐ and time‐scales approach those of continental tectonics, potentially alleviating issues with diagenetic space and time limitations associated with other paleo‐meteoric water proxies. Plain Language Summary: Past surface elevations are commonly reconstructed from the stable isotope ratios of oxygen and hydrogen in paleo‐precipitation. These ratios change systematically as air lifts up and over mountains and other topographic barriers. Direct samples of ancient precipitation do not exist so we rely on proxies instead. The most common proxies used are individual minerals, such as calcium carbonate, or fossils, such as leaves. We present a new approach, where we instead use the isotopic "footprint" of large hydrothermal cells associated with ancient volcanoes as a record of precipitation isotope ratios. By processing these large patterns with an inverse model to "undo" the alteration, we find that there was a large change in oxygen isotope values in precipitation between 20 and 12 million years ago in the San Juan Volcanic Field, Colorado, USA. This is consistent with surface uplift of 2–3 km over this timeframe. Unlike other isotopic proxies for paleo‐precipitation our technique captures an isotopic signal integrated over the space‐ and timescales of hydrothermal alteration, which approach those of the tectonic processes that make and break mountains. Key Points: Continental hydrothermal systems record meteoric water oxygen isotope compositions over broad space‐ and time‐scalesIsotopic alteration in hydrothermal systems in the San Juan Volcanic Field, Colorado, USA provides a test of this approachInverse modeling suggests a decrease in meteoric oxygen isotope ratios between 23 and 15 Ma, consistent with 2–3 km of surface uplift [ABSTRACT FROM AUTHOR]