Previous investigations of glacier dynamics at Tioga Pass during the Last Glacial Maximum (LGM) have produced different conclusions. A map of the LGM ice extent and flow direction (Alpha et al., 1987) illustrates a south-to-north direction of ice flow across the pass with little evidence to support this inference. Since the production of this map, unexpected glacial erratics of Cathedral Peak Granodiorite (CPG) have been noted in the vicinity of Tioga Pass, which are not consistent with the inferred flow direction. A comprehensive spatial data set of CPG erratics was collected. This data was collected between Tioga Lake and the southeastern boundary of the CPG bedrock, south of Tioga Pass. The erratics display trends of decreasing abundance from north to south, characteristic of boulder trains used to infer glacier flow patterns. Based on these trends, the erratics indicate a north-to-south flow across the pass, opposite to what Alpha et al. (1987) had inferred. This flow is determined to have originated from the eastern cirque of Mt. Conness, the northeastern boundary of the CPG bedrock. The Excel spreadsheet, “Profiler V. 2” (Benn and Hulton, 2009) was used to model the flows from Mt. Conness down the Lee Vining Canyon and the Grand Canyon of the Tuolumne River; these flows branched at Tioga Lake. The model provided insight into the ice dynamics in this region but was unable to provide insight into small flow reversals. Based on the distribution of CPG erratics, the “Profiler V. 2” analysis, past field research yielding evidence of other erratic boulder trains, a comprehensive set of striations and glacial landforms, and a plan-view map of ice coverage and flow direction at the peak of the LGM (Wahrhaftig et al., 2019), there is evidence to support the standing hypothesis that ice flowed south across Tioga Pass at the peak of the LGM, then became stagnant, with ice from Mt. Conness and Tioga pass eventually flowing into Lee Vining Canyon after peak LGM conditions receded
