In an extremely important archaeological discovery, a study published in the Proceedings of the National Academy of Sciences offers proof that native Californians consumed hallucinogens while making rock art.

Although researchers have long believed in a correlation between the ingestion of mind-altering substances and trippy rock art, until now it was just theory. A team studying the Pinwheel Cave in southern California—so named for a striking red whirligig shape painted on the ceiling—found wads of chewed-up plant matter stuffed into the cave’s ceiling crevices. It turned out to be Datura wrightii, a native plant whose shape resembles that of the pinwheel drawing.

Although scientists knew that natives were consuming the plant for its mind-altering properties, the proximity of it to the drawing reveals that it may have served as the source material for an illustration, rather than a work created in a trance state. The datura flower itself is a tightly furled bud that blossoms into a spiral pattern at night, much like the drawing on the cave ceiling.

The cave, which is located within the Wind Wolves Preserve, a 93,000-acre nonprofit preserve, was regularly used as a temporary shelter for activities and rituals, including ingesting the datura, according to the study. Research starting in 2007 found that native Californians lived there from approximately 1530 to 1890.

Pinwheel Cave, California. Interior of cave during laser scanning. Courtesy of PNAS.

Devlin Gandy, a co-author of the study, told National Geographic that earlier theories about the connection between rock art and hallucinogens were based on the idea that it “looks so surrealistic that it had to be made by someone tripping.” In fact, Gandy says, drawings like those in Pinwheel Cave may have served a more functional purpose: “Here’s the place to take datura.”

The report “suggest that the pictographs were probably not self-depictions of shamans in trance but, instead, stock iconographic images drawing upon mythology and the personifying of insects, animals, plants, and astronomical elements such as the sun.” Similarly, in the Chinigchinich religion prevalent in the area, sand paintings were not depictions of datura-induced dream states, but more general illustrations of cosmologies.