GM-66—Geology and mineral resources of Manuelito quadrangle, McKinley County, New Mexico

By O. J. Anderson, 1991, lat 35°22'30" to 35°30', long 108°52'30"to 109°00', 1 sheet with text, scale 1:24,000.

Manuelito 7½-min quadrangle, approximately 6 mi west-southwest of Gallup, is located in the northwestern part of the Zuni Basin in west-central New Mexico near the Arizona border. I-40 bisects the quadrangle from northeast to southwest, following the valley of the Puerco River. Rock outcrops in the Manuelito quadrangle range from northeast to southwest, following the valley of the Puerco River. Rock outcrops in the Manuelito quadrangle range from the Middle Jurassic Zuni Sandstone to the Tertiary Bidahochi Formation. Quaternary alluvial, colluvial, and eolian deposits blanket the bedrock along the drainages of the Puerco River and its tributaries. Extensive exposures of the Cretaceous coal-bearing Gallup Sandstone and Crevasse Canyon Formation are mapped in the east half and northwest quarter of the quadrangle. The type section for the Torrivio Member of the Gallup Sandstone is on and around the Torrivio anticline (Torrivio Mesa), which crosses the northeast corner of the quadrangle. Fourteen measured coal sections in the Ramah unit of the Gallup and in the Crevasse Canyon Formation are plotted on the map and keyed to additional data in the text. GM-66 and earlier published maps of Jones Ranch School quadrangle (GM-65, Anderson, 1989) and Vanderwagen quadrangle (GM-64, Anderson, 1990) extend investigations of Cretaceous rocks and associated coal resources to the northwest of known coal occurrences in the Zuni Basin. In addition to detailed descriptions of stratigraphy, GM-66 includes discussions of other mineral resources and regional structure, one cross section, and 13 map-unit descriptions.