The timing and uplift of the Laramide province in Western North America to current mean elevations of 2500 m continues to be a subject of great debate among geologists. Producing estimates of paleoelevation since the Laramide orogeny is one way to constrain possible histories of uplift. This study utilizes hydrogen isotope ratios of ancient meteoric water in latest Eocene and earliest Oligocene rhyolitic glass as a proxy for elevation. The proxy relies on the relationship between changes in elevation and the temperature-driven rainout of heavier isotopes from air masses as they are moved up and over orographic barriers. Glass samples were collected from the Central Rocky Mountains, Great Plains, and coastal Texas. Results of this study suggest that mixing of Pacific and Gulf coast air masses took place over these areas during the latest Eocene, and thus previous interpretations of hydrogen isotope data that assume rainout of air masses from a single source are not meaningful. The question of absolute elevations over these regions during the latest Eocene/earliest Oligocene remains open. It does, however, appear possible to investigate topographic relief and to conclude that the Central Rocky Mountain region was not significantly higher than the surrounding Great Plains.