The term "felsite" is a catch-all category for a wide range of typically light-colored, fine-to-coarse grained volcanic rock that is ubiquitous across the Big Bend and eastern Trans-Pecos. All things considered, felsite was probably the most commonly used toolstone through time of prehistoric peoples in the region. Although found to one degree or another in many volcanic exposures of the region, some of the better known source areas include the Rimrock country of the Chinati and Sierra Vieja mountain ranges of Presidio County, southern foothills of the Davis Mountains in Jeff Davis County, eastern escarpment of the Van Horn Mountains in Culberson County, and the northern rim of Green Valley in Brewster County. Felsite tends to be "clean", with few or no impurities or inclusions that might hamper the manufacture of tools, and most often occurs in large cobble to even boulder form. Its availability as large-sized raw material made this stone ideal for the manufacture of large expediency tools used for chopping, shaving, and scraping tasks.