Topography of the Southern Sierra Nevada

SEPTEMBER 2005, GSA TODAY ABSTRACT The paleoelevation of the Sierra Nevada, California, is important to our understanding of the Cenozoic geodynamic evolution of the North America–Pacific plate boundary, and the current debate is fueled by data that argue for conflicting elevation histories. The non-equilibrium or transient landscape of the Sierra Nevada contains information about both past and present controls on the topography of the range. Using geomorphology and thermochronometry, two parts of the landscape of different geodynamic significance and age can be identified: (1) a long-lived, slowly eroding low-relief highland or relict landscape, which we relate to a period of lower relief and elevation from 80–32 Ma; and (2) younger, rapidly-incising river gorges created by at least two stages of elevation and relief increase since 32 Ma. Our data argue for moderate range elevation of ~1500 m at the cessation of arc magmatism in Late Cretaceous time, followed by two events at between 32 and 3.5 Ma and since 3.5 Ma that increased the range elevation to the 4000 m observed elevation today.