The Permian Earp Formation can be divided into three members: the lower limestone member, the middle terrigenous member, and the upper interbedded clastic and carbonate member. The red chert-pebble conglomerate is a single, possibly isochronous unit, within the middle terrigenous member. Meandering streams, bringing red chert pebbles south from the eroding Naco Formation in the area of Winkelman and Superior, Arizona, deposited the conglomerate. The source of clastics in the lower limestone member seems to be in the south and southwest, probably in north-central Mexico. This member undergoes a gradational facies change eastward where, devoid of clastics, the lower limestone member of the Earp Formation is transitional into the upper part of the Horquilla Limestone of southwestern New Mexico.