By: L. F. Hintze and B. J. Hammond
This quadrangle straddles the Colorado Plateau-Basin and Range boundary and its western two-thirds includes features that are transitional between the two provinces. The oldest exposed rock is the Early Cambrian Tapeats Quartzite, which is overlain by nearly 4,000 feet of Cambrian dolomite, limestone, and shale. Ordovician and Silurian strata are absent here. Middle and late Paleozoic marine strata are present in the following thicknesses: Devonian, 700 feet; Mississippian, 700 feet; Pennsylvanian, 1,600 feet; Permian, 3,300 feet. A substantial period of erosion intervened before deposition of the marine Lower Triassic Moenkopi Formation. Another hiatus ensued before the non-marine Upper Triassic Chinle Formation was deposited. Succeeding Jurassic strata include the Moenave Formation, the Kayenta Formation, the Navajo Sandstone, and a few feet of the marine Carmel Formation. Locally, the Paleozoic and Mesozoic strata are structurally attenuated. Quaternary and Tertiary deposits are mostly surficial materials of alluvial, colluvial, mass-movement, or eolian origin, aggregating a few hundred feet at most in thickness. The most noteworthy Quaternary-Tertiary unit is the Gunlock Basalt.
Pages: 21 p.
Plates: 2 pl.
Location: Washington County
Media Type: Paper Map