GEOMORPHOLOGY AND GEOLOGIC HISTORY OF SAGEHEN VALLEY, TRUCKEE, CALIFORNIA

Geologic mapping at 1:12 000 of the Sagehen Valley, supported by LIDAR imagery, is used to delimit the age and origin of four terraces along Sagehen Creek in the northern Sierra Nevada of Calfornia. The goal is to better understand the Late Cenozoic geologic history of the valley. Stratigraphy and cross cutting relationships with lava flows and glacial deposits establish a timeline of geologic events. The terraces are numbered one to four from highest to lowest in elevation. Terraces 1 and 2 are overlain by 5.5 million year old pyroxene andesite. Sierran uplift at 3.3 Ma led to the incision of a deep canyon. The Pleistocene Donner Lake glacial deposits overlie terraces 1 and 2, but not terrace 3, providing the upper limit of the age of terrace 3. Terrace 3 is comprised of fluvial sediment that has been incised since 1880 by downcutting of the modern Sagehen Creek.