Glacial Deposits and Tephra in the Toiyabe Range, Nevada, U.S.A.

Abstract

The Toiyabe Range is a prominent north–south-trending range in the Great Basin, a region whose glacial history is poorly known. The most complete sequences of glacial deposits occur in north- and east-trending valleys in the vicinity of Arc Dome, the highest point in the range. In these valleys rock glaciers and small cirque moraines, unbreached by erosion (Group I deposits), lie a few hundred meters or less from cirque headwalls. Thick, hummocky terminal moraines, breached by stream courses but generally well preserved (Group II deposits), lie 2 to 3 km farther downvalley. In a few valleys isolated bodies of till (Group III deposits) extend up to 1 km beyond Group II moraines.

Locally reworked tuffaceous sediments recovered from Group I moraines are mostly of Mono Craters (California) origin but contain some Mazama and Inyo Craters glass. At least the Mono Craters glass shards are considered to represent an original airfall deposit, providing a minimum age of ca. 1200 yr BP for Group I deposits. The Toiyabes did not harbor glacier ice during the “Little Ice Age” of the last few centuries.

Group II deposits match the physiographic descriptions of and are considered equivalent to Tioga and Angel Lake moraines in the Sierra Nevada and Ruby Mountains, respectively. Group III correlations are uncertain. Weathering comparisons cannot be made to deposits in the other studied ranges because of the welded-tuff lithologies in the Toiyabes. Patina development and cavernous weathering of clasts are distinctly different between Group I deposits and older deposits, but there is little difference between weathering characteristics of Group II and III deposits.