Memoir 1 - Stratigraphic studies of the San Andres Mountains, New Mexico

by F. E. Kottlowski, R. H. Flower, M. L. Thompson, and R. W. Foster, 1956, reprinted 1984, 132 pp., 6 tables, 15 figs., 5 plates, 1 index.

The San Andres Mountains in south-central New Mexico expose a section of Paleozoic sedimentary rocks unrivaled in New Mexico in length of continuous outcrop and in completeness of existing time-lithologic units. The thickness, lithology, and extent of the Paleozoic strata concealed in the nearby basins can be estimated accurately from the sections in the San Andres Mountains and from known sections in more accessible areas.

The Bliss Sandstone, El Paso Group, Montoya Group, Fusselman Dolomite, Devonian formations, Mississippian formations, Pennsylvanian beds, Bursum Formation, Hueco Formation, Abo red beds, Yeso Formation, San Andres Formation, Dockum Formation, Sarten Formation, Dakota Sandstone, Eagle Ford or Mancos Formation, and Love ranch Formation were measured and described in detail in Rhodes, Hembrillo, and Ash Canyons. Rhodes Canyon, the most accessible in the range, contains the northernmost complete section. Hembrillo Canyon, though difficult of access, is in the center of the range. Ash Canyon is the southernmost accessible canyon in which the formations have escaped intense deformation and metamorphism associated with intrusion of the Organ Mountains batholith.

Paleozoic sedimentary rocks measure a total of 7,065 ft in Rhodes Canyon, 6,519 ft in Hembrillo Canyon, and 7,130 ft in the Ash Canyon-Love ranch area. Pre-Pennsylvanian sedimentary rocks thicken southward from 858 ft in Rhodes Canyon, and 1,380 ft in Hembrillo Canyon, to 1,918 ft in Ash Canyon. Eighteen mi north of Rhodes Canyon, in Sly Gap, pre-Pennsylvanian strata are 674 ft thick. Pennsylvanian sedimentary rocks thicken and thin southward, and Permian beds thin, as do combined thicknesses of Pennsylvanian and Permian strata. The Abo red beds thin markedly southward, where they interfinger with marine beds of the Hueco Formation. Triassic beds occur only north of Rhodes Pass. Rocks of Jurassic age are not present anywhere in or near the San Andres Mountains. Upper Cretaceous sedimentary rocks in the adjoining basins thin southward, though Lower Cretaceous rocks, absent near Hembrillo Canyon and northward, appear near Love Ranch, and thicken south of the range.

The porous dolomites and dolomitized limestones of pre-Devonian age thin northward beneath a relatively uniform blanket of impervious Devonian shales and siltstones, but still are 509 ft thick in Sly Gap, near the north end of the range. The lower part of the Pennsylvanian strata, from Derryan to Missourian in age, thickens southward to Hembrillo Canyon, but thins abruptly in Ash Canyon; south and east of the San Andres Mountains it again thickens, but remains relatively thin to the west. The thick Virgilian sequence of the Pennsylvanian, named the Panther Seep Formation in this report, thickens southward and is lithologically different from rocks or correlative age outside of the range. Biohermal and biostromal reefs are common in the upper part of the Panther Seep beds north of Ash Canyon.