Fine-grained yellow jasper was prehistorically one of the most commonly utilized toolstones in volcanic areas of the Big Bend region. It typically occurs as a mottled yellow and red stone and, while of excellent quality overall, has numerous impurities and inclusions. Technically it grades into aphanite, a dark-colored hornblende with a uniform texture that has no grain. Sometimes referred to as agate and/or chalcedony, yellow jasper is more commonly found in cobble and pebble form than as outcropping ledges. Some of the better known source areas include the Cathedral Mountain/Calamity Creek area, the vicinity of Bone Spring in Big Bend National Park, the general area of the southern Davis Mountains, hills surrounding Alpine Valley, and the Maravillas/Dugout Creek area—all in Brewster County.
Debitage (debris from tool making) of yellow jasper consistently occurs in varying quantities in prehistoric campsites of the Big Bend. However, while debitage may be present in relative density, there is usually a surprising scarcity of formal yellow jasper tools, such as projectile points, drills, or scrapers, accompanying the debitage. This probably results from the removal of finished pieces as yellow jasper tools were probably highly valued and curated. When found, tools of yellow jasper are usually of small size, a reflection of reuse and sharpening and of internal impurities in the stone that limited the size of pieces that could be worked. However, yellow jasper specimens are part of one known cache of fairly large bifaces—the Meriwether Cache from near Alpine. Because of its excellent quality, rare impurity-free cobbles of yellow jasper were highly prized by prehistoric Indians of the Big Bend.