Bulletin 26—Geology of the Gran Quivira Quadrangle, New Mexico

By R. L. Bates, R. H. Wilpolt, A. J. MacAlpin, and G. Vorbes, 1947, 52 pp., 4 figs., 9 plates, 1 index.

The Gran Quivira quadrangle is a rectangular area that includes parts of Socorro, Torrance, and Valencia Counties, central NM. The quadrangle covers about 980 mi2. The town of Mountainair lies just outside the area, near the center of the north boundary. Claunch is situated on the east boundary. No large towns lie within the quadrangle. The only settlements are the small communities of Abo and Scholle in the northwest part, Chupadera in the west-central part, and Gran Quivira in the east-central part.

The area is served by US Highway 60, which crosses the northwest corner; by State Highway 10, connecting Mountainair and Claunch; and by State Highway 161 from Claunch to Bingham, 6 mi south of the quadrangle on US Highway 380. A large number of secondary roads serves the farms and ranches of the area. The Amarillo-Belen line of the Santa Fe Railway crosses the northwest corner. A wide strip down the central part of the quadrangle in included in the Cibola National Forest. Gran Quivira National and State Monument, embracing about two sections of land, lies on the Socorro-Torrance County line in the east-central part of the quadrangle. Abo State Monument is situated half a mile north of US Highway 60, midway between Scholle and Abo.

The Gran Quivira quadrangle includes, in its extreme northwest corner, about 1 mi² of the alluvial plain that forms the east side of the Rio Grande valley. The boulder-strewn surface of this plain slopes gently to the west; along its eastern margin it has been dissected into low spurs separating wide shallow arroyos. The plain supports a thin stand of grass, cactus, and yucca.

East of the alluvial plain lie the Manzano Mountains. At their southern end, in the Gran Quivira quadrangle, these mountains are only 1.5 mi in width. The surface is rough, the drainage is by intermittent streams in deep canyons, and the vegetation cover is scant. The mountains are bounded on the southeast by a deep straight canyon with a high ridge on its southeast side. Extending very irregularly from the quadrangle's northeast corner to the center of the south boundary is a high escarpment with its steep slope on the north and west. This escarpment divides the main part of the quadrangle topographically into two parts- a relatively low, rough area to the west and north, and a relatively high, gently rolling area, Chupadera Mesa, to the east and south.

North and west of the Chupadera Mesa escarpment the surface is underlain by strata of limestone, gypsum, shale, sandstone, and arkose that dip gently southeastward except in the northwest corner where their dip is steep. These strata have varying degrees of resistance to erosion, and consequently the surface consists of alternating ridges and valleys. This condition is especially characteristic of the area west and southwest of Abo. Closer to the Chupadera Mesa escarpment the strata have in places been dissected into small erosion remnants held up by resistant beds; examples are the prominent buttes south of US Highway 60, some 6 mi southwest of Mountainair.

Between the Chupadera Mesa escarpment and the Manzano Mountains are three small disconnected areas of stream-worn gravels. These gravels, which rest on surfaces that bevel the tilted bedrock strata, represent remnants of an alluvial plain or pediment that was of wide extent before erosion greatly reduced its area. The surfaces of the pediment remnants are smooth and slope gently to the southeast. They support grass and scattered piñon and juniper trees. In the west-central part of the quadrangle is a group of long narrow ridges trending northeast. They range in length from less than a mile to more than 6 mi, and in width from a few tens to a few hundreds of feet. Owing to the relatively resistant character of the intrusive igneous rocks composing them, they stand from 10 to 100 ft above the surrounding surface.

The southwest quarter of the quadrangle includes the north end of a regional physiographic feature known as the Jornada del Muerto. This feature is an arid plain that extends more than 100 mi southward. The part of the Jornada lying in the area of this report is a nearly flat, treeless desert characterized by sand dunes and dry washes. It is rimmed on the west, north, and east by a low ridge that merges on the northeast with the Chupadera Mesa escarpment. Drainage east of Mountainair is by intermittent streams that flow from the Chupadera Mesa escarpment northward into sink holes. In the northwest part of the Gran Quivira quadrangle drainage is into Abo Canyon, which leaves the quadrangle 3.5 mi south of the northwest corner, cutting through a saddle between the Manzano Mountains to the north and the Los Pinos Mountains to the south. The canyon carries intermittent drainage westward into the Rio Grande valley. Drainage in the west-central and southwest parts of the quadrangle is by intermittent streams that are not tributary to a major stream but die out in the sands and gravels of the Jornado del Muerto. Major units of this drainage are Chupadera Arroyo and Arroyo Seco.