Mind-altering rock art.

Drawings on the walls of rock shelters along the Pecos River, near the Texas-Mexico border, depict scenes containing human figures, animals, and various shapes and symbols of uncertain meaning. These images portray ancient shamans performing rituals that were intended to forge connections to the spirit world, according to a number of researchers.

A new analysis of plant remains at Pecos River sites, informed by ethnographic accounts of Indian groups in that region, now imbues this ancient art gallery with a hallucinogenic glow. In many of the scenes, the shamans are surrounded by jimson weed and peyote, consciousness-altering substances that have been found in Pecos River rock shelters dating to at least 4,000 years ago, assert Carolyn E. Boyd and J. Philip Dering, both of Texas A&M University in College Station.

"We have evidence in the archaeological sediments and in the art indicating great antiquity for the use of two powerful psychoactive plants [by shamans]," Boyd and Dering conclude in the June Antiquity.

Pecos River rock art shows many shaman figures holding staffs attached to oval, spine-covered shapes that correspond to the prickly seed pods of a regional plant known as Datura, the scientists contend. In low doses, powders prepared from Datura, also called jimson weed, cause restlessness, disorientation, hallucinations, and high fever. Historical records cite widespread use of Datura by shamans in the southwestern United States and northern Mexico as early as 500 years ago.

Some Indians in that area considered peyote, a cactus that causes hallucinations when dried and ingested, to be a gift from their deer god, according to 19th-century accounts. Shamans shot arrows into the peyote cactus before cutting it up, as if it were a deer being hunted. Deer and black dots impaled by arrows appear near shaman figures in Pecos River pictures and represent peyote, Boyd and Dering argue.