Mineralization in Silicic Calderas: Questa, New Mexico and the San Juan Mountains, Colorado. Taos, New Mexico to Lake City, Colorado, July 20 – July 25, 1989

Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 320.The narrow, rugged Sangre de Cristo Mountains extend more than 300 km from east of Santa Fe, New Mexico, to near Salida, Colorado. The range is bounded on the west and southwest by the Espanola and San Luis Basins, that are part of the Rio Grande Rift zone (Plate 1, Frontispiece). The Sangre de Cristo Mountains owe their present relief largely to Neogene and Holocene uplift, but also follow closely the east flank of a now largely foundered Laramide (Late Cretaceous-early Tertiary) uplift (Tweto, 1979).The segment of the Sangre de Cristo Mountains near Taos, known as the Taos Range, contains spectacular alpine topography including Wheeler Peak (4012 m), the highest peak in New Mexico. In the vicinity of the Questa caldera, the focus of the Day 1 trip, the Taos Range is composed largely of Precambrian rocks partly mantled by mid-Tertiary volcanic rocks of the Latir volcanic field and invaded by coeval and cogenetic granitic rocks related to the caldera (Lipman, 1983; Lipman and others, 1986). Topographic relief between the highest summits and the floors of major canyons where they empty into the San Luis Valley is more than 1.5 km. Structural relief on the Precambrian surface between the crest of the range and the deepest part of the rift graben near Questa may be as much as 6-8 km (Lipman and Mehnert, 1979).