First use of name. Occurs in a vent 6 mi south of Animas stock (new), Walnut Wells quad, Hidalgo Co, NM in Pedregosa basin. Vent occupies a similar position in the stratigraphic volcanic sequence of the region as Animas stock--two bodies are regarded as penecontemporaneous, and derived from same magma. Is of Tertiary age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Named for exposures in secs 8, 9, 17, and 18, T31S, R18W, west-central part of Walnut Wells quad, Hidalgo Co, NM in Pedregosa basin. Geologic map. Is a plug intrudes Bennett Creek Breccia (new), and is disconformably overlain by Gillespie Tuff (new). On western side is bordered by Cedar Hill Andesite (new) and on eastern side by Basin Creek Tuff (new). Body is nearly 2 mi in diameter and exposed over a 1,000-ft vertical range. Is a monzonite porphyry, light grayish green with red color bands; at a distance, outcrop looks red. Has 20-45 percent phenocrysts in an aphanitic matrix. Jointing not well developed. Xenoliths lack contact effects. Along eastern side, rock is brecciated and shows slickensides along minor faults. Fairly resistant to erosion--shows greater relief than most surrounding rocks. Weathers to tabular blocks which form talus deposits on moderate slopes. Was probably emplaced at shallow depth--is likely that the magma filled an open vent blown out of the quartz latite extrusives. Mineral content similar to Animas stock; they probably derived from same parent magma, and deposited simultaneously. Is Tertiary in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).