Black Rocks Protruding Up: the Navajo Volcanic Field

—The mid-Tertiary-age volcanoes, dikes, and sills of the Navajo volcanic field are classic and geologically-distinctive landforms of the Colorado Plateau. They are the products of structurally-controlled magma ascent, explosive eruptions, and deep post-eruptive exhumation. Igneous rock types include potassic lamprophyres, serpentinized tuffs, and exotic mafic and ultramafic intrusives. These rocks, along with a variety of crustal and mantle xenoliths that they have brought to the surface, have been used to map the petrology and history of the lithosphere and upper mantle beneath the Colorado Plateau. The landforms of the Navajo volcanic field also figure prominently in the empirical knowledge and culture of the indigenous Navajo people. FIGURE 1. Location map of the central Navajo volcanic field, after Smith and Levy (1976) and McGetchin et al. (1977). Dark circles indicate minettes; open triangles represent SUMs. Monoclines are indicated by heavy lines. Abbreviations: AP, Agathla Peak; AZ, Arizona; BB, Boundary Butte; BP, Buell Park; CO, Colorado; CRM, Comb Ridge Monocline; CV, Cane Valley; EDM, East Defiance Monocline; GN, Green Knobs; GR, Garnet Ridge; ME, Mule Ear; MHM, Mesaverde Hogback Monocline, MR, Moses Rock; NM, New Mexico; RM, Red Mesa; SR, Ship Rock; UT, Utah. Major communities are also shown.