During pluvial periods of the Pleistocene and Holocene, a large river flowed south from Owens Lake to China Lake between the Sierra Nevada and the Coso Range. The most recent channel, dry during historic time, is clearly marked by cliffs and falls. An older, now-abandoned part of the channel beneath Pleistocene lavas east of the present course is inferred from a meander-shaped ridge in Mesozoic basement rocks and a strong positive magnetic anomaly, presumably produced by a wedge of canyon-filling basalt. Three cycles of eruption and stream erosion have occurred along the present course. The first resulted when water impounded by damming of the now-abandoned eastern course found its way along the west margin of a basalt flow at the base of the Sierra Nevada escarpment, eventually carving a canyon at least 150 meters deep. Subsequently, two cycles, each consisting of an intracanyon basalt flow followed by major stream erosion, modified this canyon to its present configuration. A potassium-argon age of about 440000 years before present for the oldest of the three eroded lavas indicates that the river was not diverted from its easterly course until after that time. The age and character of lacustrine deposits in Searles Lake, a downstream part of the same drainage system, indicate that the greatest discharge of the river, and therefore, erosion of the two younger lavas since 440000 years B.P., probably occurred between 130000 and 10000 years B.P. An estimate of the rate of erosion during this period of time together with loosely constrained potassium-argon ages for the basalt of intermediate age suggests that the youngest lava is probably a few tens of thousands of years old and the intermediate lava somewhat less than 100000 years old. The youthfulness of the youngest basalt suggests that a fourth cycle of an intracanyon lava flow followed by stream erosion is a likely event for the near geologic future.
