The Devil's Mouth Site is the desert twelve miles northwest of Del Rio in southern Val Verde County. It is directly northwest of the spot where the Devils River flows into the Rio Grande; the site has been covered by the waters of Amistad Reservoir. The site is made up of many layers of prehistoric camping debris within an alluvial terrace of the Rio Grande that was fifty feet above water level before the river was impounded. The terrace extends 150 feet southward from a high limestone cliff toward the Rio Grande and runs 1,000 feet along the edge of the river.
Scientific investigations at the site were carried out by the Texas Archeological Salvage Project (now the Texas Archeological Survey) of the University of Texas in 1959, 1961–62, and 1967. Controlled excavations into the terrace surface were made to recover prehistoric stone artifacts and flint (chert) chipping debris, soil samples with fossil pollen grains, and bone fragments from animals killed for food. Large cuts were also made with earth-moving equipment to expose and correlate deeply buried zones. The ancient vegetation and climate of the area were reconstructed by studies of fossil pollen and by analyses of alluvial sediments and buried erosional surfaces. At the end of the last, or Wisconsin, Ice Age, around 10,000 years ago, the Devil's Mouth site was a gravel bar and bedrock exposure only a few feet above river level. Periodic flooding gradually deposited layers of silt and sand, slowly raising the site's surface. The climate during this epoch was cooler and wetter than today, and piñon and grasses were more common in the surrounding desert than later.
Around 7000 B.C. the first prehistoric Indians camped at the site, leaving chert knives, scrapers, and long spear points of a type called Golondrina. A few points with a basal tang for attachment to the spear shaft were also made during this period. Lightweight spears with such points were propelled by throwing sticks (atlatls) rather than by hand and struck with great force. Deer, smaller animals, and some wild plants were apparently the main food items.
From 7000 until around 2300 B.C. the terrace continued to build upwards, while the climate gradually became drier and warmer. Successive soil layers contained short, barbed spear points in the lower zones and points of the Pandale type in the higher strata. The latter style is twisted longitudinally like an airplane propeller. A few milling stones (manos and metates) from these zones indicate that desert seeds were now being collected and ground into flour. Around 2300 B.C. heavy floods washed away part of the terrace on the southeast, nearest the junction of the two rivers. An arid climatic period with severe but infrequent rains and devastating runoff is thought to be responsible.
From 2300 B.C. onward the terrace gradually increased in height, while the climate apparently became slightly less arid, although the local vegetation was still typical of a desert. A brief return to cooler and moister conditions around 500 B.C. was followed by a warming and drying trend that continues today. The people who camped at the site after 2300 B.C. left behind layers of fire-cracked limestone from hearths used to bake such desert plants as sotol and lechuguilla. They also left a succession of many dart-point styles, from barbed and tanged forms called Shumla and Langtry to such later styles as Montell, Ensor, and Frio. Seed-grinding stones, as well as chert knives and scrapers, continued in use. Small chert arrow points and rare fragments of earthenware pots, both from after the time of Christ, appear in the topmost strata of the terrace.
The local artifact assemblage, with the possible exception of the early Golondrina material, belongs to the prehistoric desert cultures that stretched across the American Southwest, western Texas, and northern Mexico after the Ice Age. The Devil's Mouth Indians adapted their economy to hunting small game and gathering wild plants in an increasingly arid environment and lacked permanent housing or agriculture.
The Devil's Mouth Site is one of the first deep-well-stratified archeological sites to be excavated and reported in western Texas, as well as the first to yield a long record of vegetational and climatic change from pollen studies. Golondrina and early tanged and barbed projectile points were first found in a good stratigraphic context at this site. The artifacts and site records are housed at the Texas Archeological Research Laboratory of the University of Texas at Austin.