Many of the Cretaceous limestone formations in the southeastern Trans-Pecos are chert bearing. "Edwards chert" is the generalized term for these materials. High quality gray chert appears to have been a preferred toolstone during much of the region's prehistory. This inference is based in part on the fact that at least three of only known stone caches from the Big Bend (McHam, Lizard Hill, and Limpia Creek caches) are composed almost entirely of gray limestone cherts--this in spite of the fact that the region is replete with other high quality, workable stone types.
Sources of gray chert, including Edwards Chert, from the region include the western Stockton Plateau, Del Norte Mountains, Glass Mountains, Apache Mountains, and remnant limestone outcrops in scattered localities within primarily volcanic areas. When locally available, gray cherts were commonly used through time in the production of relatively small, formal chipped-stone tools such as projectile points, end and side scrapers, perforators, and knives.