Koley Black group (Cold Mesa; Channel No. 37), Agathla Peak (El Capitan), Mineral Mining District, Navajo County, Arizona, USAi

Regional Level Types
Koley Black group (Cold Mesa; Channel No. 37)	- not defined -
Agathla Peak (El Capitan)	Peak
Mineral Mining District	Mining District
Navajo County	County
Arizona	State
USA	Country

The Koley Black area is known by various names, as a result of the great interest displayed in it by both geologists and prospectors. In this report it is referred to as the Koley Black area, after the name of the original claimant. During a U.S. Atomic Energy Commission Airborne Radioactivity Survey in the Monument Valley area (Winthrop L. Cummings, written communication, 1952), two anomalies were recorded over the Koley Black area. Each area of anomaly was named; one is known as "Cold," the other as "Sheep." The area known as "Cold" is shown on figure 12 as channel 45. It is uncertain which of the remaining channel outcrops is known as "Sheep"; likely it is channel 44. At the time of its drilling program in the Monument Valley area, the U.S. Atomic Energy Commission named the area "Cold Mesa."

The Koley Black area, at lat 36°48'12" N., and long 110°09'18" W., is in Navajo County, Ariz., about 3 miles southeast of Agathla Peak and a similar distance due north of the Porras Dikes. The area is about 8 miles northeast of Kayenta, Ariz. Consolidated sedimentary strata exposed in the Koley Black area range from the De Chelly sandstone member of the Cutler formation, under the valley floors, to the Shinarump member of the Chinle formation, which forms the general upland surface. The Shinarump member in this area is about 25 feet thick, although it thickens to 45 feet or more as a result of channeling. In places on the upland surface the Shinarump member thins laterally as a result of erosion; in these localities the underlying Moenkopi formation forms the surface.

The ground surface is veneered by a thin mantle of sand that thickens locally to 5 feet or slightly more. In places, irregular hummocks of the Shinarump member rise 20 to 30 feet above the general ground surface.The area is on the south flank of the Agathla anticline, and the strata dip about 5° to the south.

A maze of channels is exposed in this area. They range in width from channels 35 feet wide to others that exceed 250 feet in width. The major geologic problem, as shown in figure 12, has been to relate the 4 channels noted in the southeastern part of the area to the 7 channels in the north western part. Data on the channels are given in table 1. All the channels strike northwest, and this suggests that they all may be part of the same channel network. In general, the larger channels are in the southeastern part of the area, and it appears probable that one or more of these larger ones may have branched to form the smaller channels.

Sedimentary rocks filling the channels are coarse conglomerate beds near the base which grade upward into conglomeratic sandstone and coarse-grained sandstone beds near the top. Silicified wood is buried in channel strata as fragments and as logs as much as 2 feet in diameter. Also included are small pod-shaped masses of a black, coaly substance (vitrain?) surrounded by conglomeratic sandstone. Limonite stains the surface of the channel fill but does not appear to have penetrated the sandstone.

The Koley Black channels are underlain by a green to light-gray altered zone about 1 foot thick in the uppermost siltstone beds of the Moenkopi. The altered zone thickens slightly below the channels. Four of the Koley Black group of channels contain small amounts of copper in basal channel fill.