This outcrop is part of the Papago Park pediment exposed in central Phoenix. It is the Barnes Butte Breccia Member of the Neogene Camels Head Formation. - Reddish brown, coarse-grained, poorly sorted and stratified, massive, arkosic breccia with subangular to angular clasts ¼ inch to 15 feet in diameter (0.7 cm to 4.5 m), slightly imbricated; composed of granite (70 to 85%) and metarhyolite (10 to 20%) in a matrix of rock fragments and iron-oxide cement.
T.L. Pewe, C.S. Wellendorf and J.T. Bales, 1986, Geologic Folio of the Tempe Quadrangle, http://repository.azgs.az.gov/uri_gin/azgs/dlio/1413