Considerable interest and debate surround the problem of uplift and geomorphic evolution of areas undergoing arc magmatism and arc accretion to continental margins. The Sierra Nevada of California, a deeply eroded remnant of a late Mesozoic magmatic arc, has conventionally been thought to have been uplifted in late Cenozoic time, however this conclusion has been challenged by low temperature geochronologic studies suggesting high relief as early as late Mesozoic. This project will measure river incision rates in the Sierra Nevada by comparing elevations of dated cave deposits with present day river elevations. These data will be incorporated in a model of Sierra landscape evolution in order to provide a test of the competing mutually exclusive hypotheses. Results will be of considerable regional importance and have clear implications on broader issues.