This paper is the result of observations made at intervals from 1921 to 1951 at Crater Mound, 20 miles west of Winslow, Arizona. The regional and the local studies of the geology furnished information which supports a geologic origin for Crater Mound.

Crater Mound occurs exactly on the axis of the large northwest-trending Sunshine Nose. The long axis of Crater Mound and the axis of Sunshine Nose both strike N. 8° W. A ring syncline with a drainage outlet toward the northeast lies outside and around the rim from 12 to 34 mile from the center of the crater. Within the mound, two grabens (down-faulted blocks) occur, one on the northwest, one on the southeast end, both part of a single large graben across the top of the crater. The graben pattern along with sink holes is common in the area. Also, the similarity of the Crater Mound graben to some of the graben on the faulted anticlines and domes in the Colorado Plateau is marked and suggests a possible genetic relationship.

The crater and the mound are two separate, though interrelated, geologic features. The present mound is the remnant or skeleton of an elliptical dome with a graben-like sink in its apex. Originally the dome was far higher, in the order of 1,000 feet or more above its present height. The blocks of Kaibab limestone and the Coconino sandstone which are found out of normal position above the Moenkopi redbeds fell from the overturned walls. Much of the white sand so prominent on the rim is laminated and bedded and is principally derived by weathering action from the sandy Kaibab limestone. The silica glass, lechatelierite, which occurs at Crater Mound is probably derived from old explosive volcanoes northwest or southwest of Crater Mound.

A tectonic-geomorphic origin is stressed. A deep-lying evaporite and limestone section was affected by waters infiltrating along the fault planes after the original folding and faulting occurred. Also, the disturbance of the regional water level by tectonic action accelerated subterranean erosion and stoping by solution with consequent subsidence.

A meteoritic shower occurred in the vicinity but it bears no visible relationship to the origin of the crater as the data prove that the crater was present before the meteoritic shower.

The folding is probably late Miocene or early Pliocene in age and of the order of 5,000,000 years, the crater of the order of 200,000 years or more, and the meteoritic fall that occurred in the vicinity considerably later of the order of 50,000–150,000 years.

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