WAS THERE ICE ON MOUNT TAYLOR IN THE LATE PLEISTOCENE?

Mount Taylor is an isolated, eroded composite volcano on the Colorado Plateau in northwestern New Mexico, active from >3.3 to 1.5 Ma, with a summit elevation of 3445 m. Since the general study of Ellis (1935), Mount Taylor has been identified as a site of late Pleistocene glaciation in various compilations. Ellis considered the large amphitheater on the eastern face of the mountain to have held ice, but this area shows no evidence of cirque development or other clear glacial erosional or depositional features. A valley with more cirque-like morphology lies just NE of the north summit of Mount Taylor, known as La Mosca Peak (3360 m). We identified a series of three possible bouldery terminal moraines within this valley between 3080 and 3140 m elevation, and surveyed profiles across them. The 5 to 9 m-high distal slopes have angles of about 22-28°, similar to slope height-slope angle relations for late Pleistocene moraines elsewhere in the Rocky Mountains. Ridgecrests are subdued, and proximal slopes are roughly horizontal or slope very gently downvalley, suggesting that if the features are moraines, upvalley areas (which are not bouldery) have later been infilled by alluvium. Lateral moraines are not obvious, and we cannot rule out the possibility that the steep bouldery fronts represent rock glacier toes or mass movement features.

A reconstructed equilibrium-line altitude (ELA) for the possible La Mosca Peak glacier lies at ~3190 m. Although Mount Taylor’s isolated location makes comparisons difficult, this is similar to (1) the lower range of ~3150-3450 ELAs reconstructed for other small late(?) Pleistocene glaciers with N to E aspects in the Sangre de Cristo Range, 175-200 km to the northeast, and (2) ca. 3160 m ELAs in the White Mountains of Arizona 230 km to the southwest (this study); and (3) ELAs from 3140-3400 m at the San Francisco Peaks composite volcano, 360 km to the west (Poellot, 2001). Further work will evaluate whether more direct evidence of glaciation exists on Mount Taylor. Unfortunately, the friable trachytic volcanic rocks of Mount Taylor do not readily preserve striations, but we have not yet conducted an intensive search at the time of this writing.