Stream incision, tectonics, uplift, and evolution of topography of the Sierra Nevada, California

Stream incision, faulting, thermochronologic, and geobarometric data suggest that Sierra Nevada topography is a consequence of two periods of uplift. Stream incision of up to 1 km has occurred since similar to5 Ma. Maximum Eocene-Miocene incision was 150 m. Uplift of the Sierra Nevada, westward tilting, stream incision, and east-down normal and dextral faulting along the present eastern escarpment of the range began at similar to5 Ma. Estimates of Late Cenozoic crestal rock uplift for different areas in the Sierra Nevada range from 1440 to 2150 m. Low summit erosion rates suggest that the rock uplift approximates the surface uplift of crestal summits. Tertiary stream gradients were lower than modern ones, suggesting that the bottoms of the canyons have been uplifted in the Late Cenozoic and that the mean elevation of the Sierra Nevada has increased. The elevation of pre-Cenozoic basement rocks above the base of Tertiary paleochannels ranges from <200 m in the northern part of the range to >1000 m in the south, and shows that significant relief predates Late Cenozoic incision. Elevations at similar to5 Ma (before Late Cenozoic uplift) may have been <900 m in the northern Sierra and >2500 m in the southern Sierra. Minimal Eocene-Miocene stream incision suggests that paleorelief and paleoelevations are relics of pre-Eocene uplift. Reduction of elevation and relief following pre-Eocene uplift may have coincided with eclogitic recrystallization of the mafic root of Sierran batholith. This eclogitic keel may have foundered in the Late Cenozoic, triggering uplift.