A LATE PLIOCENE TO MIDDLE PLEISTOCENE PLUVIAL LAKE IN FISH LAKE VALLEY, NEVADA AND CALIFORNIA

The question of whether a pluvial lake existed in Fish Lake Valley, Ne vada and California, has been debated for more than 100 yr. New strati graphic evidence indicates that a lake did exist in this valley at int ervals during late Pliocene to middle Pleistocene time. This lake may have drained northward, or it may have been periodically contiguous wi th a pluvial lake to the north in Columbus Salt Marsh. Proof of the ex istence of this lake, informally named Pluvial Lake Rennie, is derived from three principal outcrops of shallow-water deposits, two outcrops of deep-water deposits, and several drilling logs. The deposits conta in beds of silicic tephra, which provide age control. On the basis of thickness, grain size, major-oxide chemistry of glass shards, and pale omagnetism, three of the shallow-water deposits, including deltaic(?), beach, and siliceous hot-spring sediments, consist mainly of Bishop a sh derived from the 0.77 Ma eruption of the Long Valley caldera. A fou rth shallow-water deposit(?) is associated with approximately 1 Ma Gla ss Mountain tephra beds. The exposed deep-water deposits consist of gr een claystone, siltstone, and fine-grained sandstone containing tephra derived from the eruptions of the approximately 2.1 Ma tuff of Taylor Canyon and the approximately 2.0 Ma Huckleberry Ridge Tuff. The drill ing logs record numerous thick beds of clay and sandy clay inferred to be deep-water lacustrine deposits. Pluvial Lake Rennie fluctuated in size and depth beginning prior to 2 Ma and continuing until sometime a fter 0.77 Ma. At about 0.77 Ma, the lake had a highstand at an elevati on of approximately 1,460 m, covered an area of 400-500 km2, and had a maximum depth of approximately 250 m. The lake level dropped just aft er the eruption of the Bishop ash, but the lake may have persisted at a lower level until approximately 0.5 Ma. No large, long-lived lake ex isted in Fish Lake Valley in late Pleistocene time, probably due to th e increasing rain-shadow effect caused by the relative uplift of the W hite Mountains and Sierra Nevada in the Pleistocene. These results ind icate that the late middle to late Pleistocene history of Pluvial Lake Rennie is similar to that of Lake Tecopa but is quite different from those of Lake Lahontan and Searles Lake.