RECONSTRUCTION OF AN EARLY MIOCENE RIVER CHANNEL IN THE EASTERN SIERRA NEVADA BY CORRELATION OF VOLCANIC DEPOSITS

The goal of this project was to improve upon existing geologic mapping near Buckeye Canyon, CA, (Schubert, 2017; Chesterman, 1975; Huber et al., 1989), where Miocene Stanislaus Group lavas probably flowed down a paleo-stream toward Rancheria Mountain, near Hetch Hetchy. There are few outcrops mapped along this proposed paleochannel and the existing mapping disagrees in location and formation identifications. We corrected multiple inconsistencies by mapping at a much larger scale using mobile electronic devices and GIS. Furthermore, we verified the presence of Stanislaus Group Table Mountain Formation within the map region indicating they may lie along the former paleo-stream. We ran paleomagnetic analysis on an outcrop thought to be Stanislaus Group in the Eagle Creek drainage. Alternating field demagnetization results were straightforward, precise, and consistent, but did not agree with any member of the Stanislaus Group, an angular difference of at least 30º, indicating the outcrop we sampled was not part of the Stanislaus Group. Local fault block rotation is unlikely in the map area, which lies on the stable Sierra Nevada, but is prevalent just to the east in a heavily extended region. This disputes its identification as Stanislaus Group.