RECONSTRUCTING A 10.4 MA PALEOCHANNEL OF THE TUOLUMNE RIVER USING EVIDENCE FROM GEOCHEMICAL, LITHOLOGICAL, AND PALEOMAGNETIC CORRELATION OF TRACHYANDESITES IN THE SIERRA NEVADA, CA

Channel-filling volcanic remnants of the Stanislaus Group have been studied to reconstruct the paleogemorphology of the Sierra Nevada, CA, as tilt markers and piercing points to reveal uplift and faulting, and to make inferences about the age of current Sierra Nevada topography. The Stanislaus Group is widespread, spanning 130 km across the Sierra Microplate and into the Basin-and-Range Province. Despite an absence of outcrops in the 30 km between the eruptive source at Little Walker Caldera in the Eastern Sierra Nevada and trachyandesite outcrops at Rancheria Mountain near Hetch Hetchy Reservoir, previous work on volcanic remnants at Rancheria Mountain and at Priest Measured Section near Little Walker Caldera have revealed paleomagnetic, geochronological, and some geochemical evidence of correlation, suggesting the existence of a ~10.4 Ma former paleochannel of the Tuolumne River (or a tributary) that flowed south-southwest from its eruptive source to Hetch Hetchy. Recent mapping and new evidence from geochemical and thin section analyses of archival samples from Rancheria Mountain have further confirmed the existence of the former paleochannel and have allowed for more detailed correlation. The normal polarity trachyandesites are consistent with the upper flows of the Lower Member and Large Plagioclase Member at Priest Measured Section. This work establishes the locality as a tilt marker for further studies on Sierra Nevada tectonics.