Pleistocene latite and basalt flows crop out along the Upper Truckee Canyon, located immediately downstream from Lake Tahoe, and throughout the Truckee Basin, an intermontane basin at the north end of the canyon. They were extruded over a topography somewhat similar to that of the present from numerous, widely spaced vents.
The flows postdate the major part of the Pliocene-Pleistocene deformation of the Sierra Nevada and appear to predate the oldest recognized glaciation in this part of the Sierra Nevada. They are correlated with the Lousetown Formation of western Nevada.
Large-scale deformation followed the volcanism. During upwarping of the area east of the Truckee Basin, the Truckee River maintained an antecedent course and eroded a deep canyon. Because no sediments in the Truckee Basin can be correlated with this period of uplift, it is concluded that the cutting of the canyon proceeded at a rate equalling or exceeding that of the uplift. All movements appear to predate the oldest recognized glaciation.