The paleorelief of mountain belts can be estimated from the d18 O value of authigenic minerals. Development of relief during mountain building often creates lee-side rain shadows in which precipitation is depleted in 18 O and D. The magnitude of this rain-shadow effect is strongly correlated to relief. A compilation of d18 O data from surface waters throughout the globe shows a linear relationship between net elevation change and Dd18 O(R2=0.79). Through the use of this relationship, we investigated the timing and magnitude of elevation change in the Southern Alps of New Zealand the Sierra Nevada of California. The d18 O values of kaolinites from New Zealand show an 6\% decrease in the early Pliocene that corresponds to an 2 km elevation change in the Southern Alps. The d18 O of smectites from theSierra Nevada show little change since 16 Ma, suggesting that these mountains have been a long-standing topographic feature.