Cenozoic structural geology of the central Cimarron Range, New Mexico
— Craig S. Goodknight

The Cimarron Range, in Colfax County, New Mexico (Fig. 1) is a southeastward-extending spur of the southern Sangre de Cristo Mountains. The range is bordered on the west by the down-faulted Moreno Valley, on the east by the Raton basin and on the south by the lava-covered Ocate Plateau. Elevations within the Cimarron Range vary from about 7,500 ft (2290 m) to nearly 12,500 ft (3810 m). Accessibility to the central part of the range is provided by U.S. Highway 64 which follows Cimarron Creek through its scenic canyon between Ute Park and Eagle Nest. This study is based upon a masters thesis by Goodknight (1973) under the supervision of Dr. L. A. Wood-ward of the University of New Mexico.

 

Previous work in the area was conducted by Ray and Smith (1941) and Smith and Ray (1943), who described the geology of Moreno Valley and the Cimarron Range, respectively. Wanek and Read (1956) briefly discussed the area and suggested a "diapiric plunger" origin for the Cimarron Range, and Robinson and others (1964) described and mapped all of Philmont Scout Ranch and part of the surrounding area. Baltz (1965), in a report on the stratigraphy and paleotectonics of the Raton basin, postulated the existence of a Paleozoic positive area east of Eagle Nest, which he referred to as the Cimarron arch. Simms (1965) mapped and described the stratigraphy and structure of the Rayado area, which generally includes the southern Cimarron Range. Clark (1966) mapped and described the geology and ore deposits of the Eagle Nest quadrangle, to the west of the Cimarron Range.

 

Superficially, the Cimarron Range is a north-plunging anticlinal mountain mass on which sedimentary rocks dip off a Precambrian core eastward into the Raton basin (Clark, 1966). The core of the central and southern parts of the Cimarron Range consists mainly of a vertically uplifted mass of Pre-cambrian metamorphic rocks bounded on its eastern side by an upthrust reverse fault, which gradually steepens from moderate-angle at the surface to nearly vertical at depth. North of Cimarron Canyon the range consists mainly of a thick stack of igneous sills of mid-Tertiary age which spread apart Paleozoic and Mesozoic sedimentary rocks.

 

The Laramide orogeny is responsible for the major structural features of the southern Sangre de Cristo Mountains, but Laramide deformation is not apparent in the Cimarron Range north of Cimarron Canyon. South of the canyon, however, the range is well-defined on its eastern edge by the Fowler Pass fault, an upthrust of Laramide origin. The entire range was affected by late Tertiary high-angle faulting along its margins.