Precambrian deformational history of the Picuris Mountains, New Mexico
— Kent C. Nielsen and Scott, T. E., Jr.

The Picuris Mountains are located in north-central New Mexico approximately 20 km southwest of Taos (fig. 1). These deformed and metamorphosed Precambrian rocks form a wedge-shaped basement high which extends 26 km west-southwest from the main body of the Sangre de Cristo Mountains. To the north and west are Tertiary sedimentary and volcanic rocks of the San Luis Valley. To the south, Tertiary sedimentary rocks of the Espanola basin separate the Picuris Mountains from other Precambrian rocks (Manley, 1979). To the east, upper Paleozoic sediments of the southern Sangre de Cristo Mountains rest unconformably on Precambrian units. At the eastern edge, the Picuris Mountains are 16 km wide including associated Paleozoic units, but taper to a point near Dixon (fig. 1). In profile, the range consists of three topographic steps with the lowest step in the west. Each step is related to a northwest-trending fault along which part of the movement is down to the west (fig. 2). A more complete description of the physical features is given by Montgomery (1953, p. 2-4).

 

Since Just's (1937) and Cabot's (1938) early reconnaissance surveys, significant progress has been made in the understanding of Precambrian rocks of northern New Mexico, particularly in the Picuris Mountains. Montgomery (1953) produced an excellent regional map, stratigraphic succession and petrologic description of the Picuris Mountains which has served as a basis for the more recent detailed work. Montgomery's report was revised in a much broader work by Miller and others (1963). Nielsen (1972) proposed a deformational history based on mesoscopic structural analysis and mineral paragenesis. Long (1974, 1976) subdivided the intrusive rocks into four magmatic events (spanning a minimum of 300 m.y.) based on field relationships, composition and available isotopic data. Most recently, Holdaway (1978) has analyzed metamorphic assemblages to determine equilibrium pressures and temperatures of metamorphism. Isotopic studies by Fullagar and Shiver (1973) and Gresens (1975) provide a time reference which, in combination with the other data, yields a coherent general picture of Precambrian history from approximately 1800 m.y. B.P. until 1200 m.y. B.P.