Cienega Brown Chert

Cienega brown chert, a name coined here, comes from the panhandle of Big Bend Ranch State park (BBRSP) in Presidio County. It has been found in a single location immediately adjacent to an alkali basalt or hawaiite dike that lies perpendicular to Cienega Creek, southwest of the Cienega Mountains. The dike in this area has cut through a deposit of air fall tuff, which, among other things, includes Cretaceous sedimentary rocks (which, in this case, includes chert). Two documented outcrops of the Cienega brown chert occur in this location, both about a meter in diameter.

This material was sought after by prehistoric peoples because it has been naturally heat treated by volcanic activity. Technically a metamorphosed rill, brown chert was “baked” when heated by molten igneous material flowing through cracks in the surrounding limestone within which the chert had originally formed. This gave the chert a glossy brown sheen and improved its quality, making it easier for prehistoric peoples to knap. A Folsom point made of this material and found within a kilometer of the quarry shows that the source area was known by early Paleoindian times. Undoubtedly later peoples continued to make use of the material as well, as the outcrop area is strewn with flakes and chips of this distinctive stone.

photo ofCienega brown chert from Big Bend Ranch State Park
Cienega brown chert from Big Bend Ranch State Park. Cienega brown chert is naturally heat treated by volcanic activity, improving its quality and giving it a glossy brown sheen. Photo by Steve Black.
photo of outcrop of Cienega brown chert in Big Bend Ranch State Park
Outcrop of Cienega brown chert in Big Bend Ranch State Park. This stone has been found in a single location in the park’s panhandle near Cienega Creek, southwest of the Cienega Mountains. Photo by Logan McNatt, courtesy Texas Parks and Wildlife Department.
photo of the base of a Folsom point made from Cienega brown chert.
Base of a Folsom point made from Cienega brown chert. Cienega brown chert is a high quality stone that was sought after by prehistoric peoples. Photo by John Seebach, courtesy of CBBS, Sul Ross State University.