Quaternary stratigraphy, geomorphology, and hydrologic history of pluvial Lake Madeline, Lassen County, northeastern California

During Pleistocene pluvial periods, Lake Madeline occupied an isolated, internally drained volcanic plateau comprised of three contiguous subbasins: Grasshopper Valley, Dry Valley, and the Madeline Plains in northeastern California. The geomorphic expression and areal extent of lake deposits reveal that pluvial Lake Madeline achieved maximum lake levels prior to late-middle Pleistocene (130 ka) and later experienced several minor fluctuations before reaching its late Pleistocene highstand about 23 ka. Shoreline correlations and relative age assignments are enhanced by a numerical age on the Trego Hot Springs tephra (~ 23.2 14C ka B.P.) recovered within the study basin. Stratigraphic correlation of lacustrine strandlines and channel geomorphology strongly suggests that overflow of pluvial Lake Madeline occurred prior to the last glacial maximum. This lake overflow created a hydrologic connection with Secret Valley and the Honey Lake segment of Lake Lahontan to the south. This physical evidence indicates that a 25% decrease in effective moisture has occurred from the middle to late Pleistocene in this paleolake of the northwestern Great Basin.