Is youngest (of three) basaltic to latiandesitic effusive rock unit mapped in western part of Raton-Clayton volcanic field, Colfax Co, NM in Las Vegas-Raton basin. Flows, where not mantled by ash, generally are only sparsely vegetated, have rough clinkery and spinose surfaces, and commonly have tumuli on their surfaces. Steep-flanked cones range in height from a few hundred ft to 1,500 ft and are composed of ash, scoria, bombs, and blocks. Rocks are strikingly inhomogeneous; they range from andesibasaltic to lati-basaltic, with some alkali basalt. Phenocrysts consist of olivine (about 2 percent), augite (o.5 percent), and rarely hypersthene. Groundmass is holocrystalline and consists of plagioclase, augite, olivine, and opaque oxide. Xenocrysts are quartz (3.1 percent) and feldspar (0.3 percent). Petrography and petrochemistry described. Radiometric age ranges from 2,400-8,000 yrs. Age is Holocene.

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