Was Mount Taylor glaciated in the Late Pleistocene? An analysis based on field evidence and regional equilibrium line altitudes

Abstract

Since reconnaissance work in the early 20 th century, the existence of Pleistocene glaciers on Mount Taylor has been recognized in compilations of Rocky Mountain glaciation. This eroded composite volcano stands alone as the most prominent topographic element of the Colorado Plateau in west-central New Mexico. Its highest elevations, however, rise only a few hundred meters above the lowest late Pleistocene equilibrium line altitudes (paleo-ELAs) in the region, and potential cirques on the mountain are at best weakly developed. The valley head most likely to be a cirque lies just northeast of La Mosca Peak. We found possible terminal moraines in this valley floor; alternative interpretations of these bouldery features as rock glacier toes or landslide deposits appear less probable, but cannot be ruled out. A search for striated clasts or bedrock in this area was unsuccessful, but fractured andesitic rocks such as those on Mount Taylor do not typically preserve such features. Using the possible moraines to reconstruct a small cirque glacier yields an equilibrium line altitude of approximately 3,220 m by the accumulation area ratio method, within the regional range of paleo-ELAs. Pleistocene glaciation on Mount Taylor remains uncertain, but is unlikely to have occurred for any significant period in the eastern amphitheater of the mountain where it was previously inferred.