Proterozoic rocks of the Taos Range, Sangre de Cristo Mountains, New Mexico
— Reed, John C., Jr.

Proterozoic basement rocks in the core of the Taos Range are invadec by Tertiary plutons and are partly mantled by Tertiary volcanic rocks related to the Miocene Questa caldera. Laramide thrust faults and highangle faults related both to the Rio Grande rift and to the Questa calden cut the basement rocks (Lipman, 1983). The Proterozoic rocks include supracrustal rocks of volcanic, volcaniclastic, and sedimentary origins and a variety of plutonic rocks, all of which have undergone amphibolite- grade regional metamorphism. Most of the rocks have conspicuous foliations; many have distinct mineral lineations produced by shearing and recrystallization during and after metamorphism.

Much of the Taos Range (Fig. 1) was mapped by McKinlay (1956, 1957) and Clark and Read (1972), but these studies did not focus on the Precambrian rocks. Condie (1980) made a reconnaissance of the Precambrian rocks in the southern part of the range, and McCrink (1982) and Condie and McCrink (1982) published a detailed description and geochemical study of the well-exposed sequence of supracrustal and intrusive rocks in the Gold Hill—Wheeler Peak area. Mapping of the Precambrian terrane by the U.S. Geological Survey began in 1980 in conjunction with a long-range study of the Questa caldera and as part of the evaluation of the mineral-resource potential of Wilderness and Wilderness Study Areas in the Tans Range. A nreliminary man of the southern part of the range has been published (Reed and others, 1983) and a map of the entire area is in preparation. A few preliminary lead— uranium ages are available on zircon from the Proterozoic rocks. All the ages quoted in this report are from Bowring and others (1984) except as noted. The uncertainties in the ages quoted are generally less than 10 m.y. A paper fully reporting the analytical results on which the ages are based is currently in preparation.