Rock glaciers in the San Mateo Mountains, south-central New Mexico

Two types of rock glaciers of Wisconsin age occur on the northern slopes of the highest peaks. Tongue-shaped rock glaciers, 300-800 feet long, occur in cirques. Lobate rock glaciers occur at the base of talus slopes on the valley sides, and are smaller. Both are characterized by well-defined longitudinal and transverse ridges. The rock glaciers have elevations of about 9,000 feet and are composed of angular and subangular blocks of rhyolite with average lengths of 3-4 feet. The debris is stabilized, and most surfaces are free of vegetation except for lichen. Regional studies show the rock glaciers to be nonglacial in origin; the rock masses are thought to have moved because of flow of interstitial ice. The tongue-shaped ones developed from coalescing protalus lobes, whereas the lobate glaciers formed from individual protalus lobes.