Bulletin 70—Geology of the Knight Peak area, Grant County, New Mexico

By D. L. Ballmann, 1960, 39 pp, 3 tables, 10 figs., 1 plate, 1 index.

Precambrian granite, intruded by dikes of Precambrian diabase, is present on the northeast and southwest sides of the Knight Peak area. Outliers of Cambrian–Ordovician Bliss Sandstone and Ordovician El Paso Limestone, of approximately the same thickness as these same units elsewhere in the Silver City region, suggest that the uplift of the Big Burro Mountains did not begin in Precambrian time.

An arkose, possibly of the Lobo Formation of Cretaceous age, is present locally above the Precambrian granite.

Tertiary volcanic rocks, consisting of a lower rhyolitic series of lavas, tuffs, and agglomerate, early andesitic lava and tuff, and middle rhyolitic breccias, lava, and tuffs, accumulated to a thickness of over 5,000 ft Andesite was intruded locally along minor faults. Two large perlite bodies are among the early rhyolitic rocks.

Erosion in nearby areas furnished detritus for the lower beds of Gila conglomerate. Faulting along the Taylor fault on the northeast side of the area began at this time. Continued downward movement along this fault produced a basin in which the upper beds of the Gila accumulated. Greater displacement in the northern half of the area produced hinge faulting along the Malone fault, which bounds the northern half of the area on the west.

Several phases of late volcanic activity in Quaternary time produced rhyolitic cones and intrusive bodies, dacite lava, and andesitic lava and tuff, which overlie the tilted rocks of the Knight Peak area with an angular unconformity. Later Quaternary events include the deposition of high-level gravels, pediment gravel, and alluvium. Dissection of the mountains and some crossfaulting continue to the present.