NATURE NOTES:
In “Bedrock Features,” West Texas Prehistory Is Etched in Stone

By Andrew Stuart

Often overlooked, they’re among the most abundant signs of our region’s ancient human past. To encounter one in a remote corner of West Texas – the caprock canyons, the Devils River, the Big Bend desert – is to be reminded how thoroughly this land has been lived in.

“Ground-stone bedrock features” are holes in stone that prehistoric peoples used to prepare food. From shallow depressions in boulders to deep mortars in limestone shelves, there are tens of thousands in West Texas. 

Archeologist Amanda Castañeda analyzed more than 800 bedrock features in the Lower Pecos canyonlands. Her work sheds new light on a technology at the heart of ancient life.

Their use was global. From the Americas to Asia, prehistoric peoples chipped holes in boulders or bedrock. With another stone, or “mano,” food was crushed, ground or mixed in these holes.

“Think of a modern-day molcajete or mortar and pestle, like you see on the pharmacy symbols,” Castañeda said. “They’re kind of an all-purpose tool or technology that prehistoric people would have used to crush up their food, whether it be bone or animals or plants – a really large variety of things.”

Archeologists once thought mortars were worn to different depths through use. But testimony from tribal peoples suggests features were fashioned with specific purposes in mind.

Using 3-D photographic technology, Castañeda analyzed 824 features from 10 sites, on the Pecos and Devils rivers, and in Eagle Nest Canyon near Langtry. She found four broad categories.

The majority – 92 percent – were less than 3 inches deep. They were likely created in a few hours. Castañeda describes these as “non-specialized.”

“A small hunter-gatherer group doing their daily business, whatever they came across that day, they could process in those shallow features,” she said. “Mesquite, prickly pear tuna fruits, hackberry, grasses, seeds, walnut. They would crush animal bones to get at the marrow. If you’re trying to make dinner for just your family, I think those features would do the job for you.” 

The second type is 3 to 7 inches deep, conical in shape. The wear suggests these were used for hard materials. A third type is similar in shape, but up to 1 foot deep. Castañeda says these mortars may have been used to crush mesquite beans into flour.

The fourth type is the rarest – and the most mysterious, and suggestive. These mortars have vertical walls, and are up to 2 feet deep.

“Those are the types of features that even when you lay down on the ground and try to stick your arm into them, you can just barely brush the bottom,” Castañeda said. “So one of my questions was, if you can hardly gather the material that you’re processing in them, what are they using them for? Why is this depth really necessary?”

One hypothesis is that baked agave – crushed and mixed with water – was placed in these holes and allowed to ferment.

“Across Mexico, in groups that did not have ceramics, they would use holes in the ground to ferment their alcohol,” Castañeda said. “So I think it’s a possibility. Think about it kind of like a margarita bowl – everyone had their river-cane straws and gathered around the bedrock mortar to get their taste of agave beer.”

Eight such features are found at a Seminole Canyon State Park site, which also contains stunning rock art. It may have been a gathering place during times of seasonal abundance.

“These sites may be those types of places,” Castañeda said, “where they would come together, have ceremonies, marry off their children, paint murals, have big feasts, ferment agave alcohol – and do all those sorts of things that humans like to do.”

Women generally did the hard work of processing plants. In some societies, bedrock features were bequeathed from mother to daughter, and could be used for generations.

Though the features are widespread, their use varied. In the Big Bend, deep holes were fashioned in open sites – perhaps for rainwater catchment.

Castañeda’s work is a foundation. Continued research could provide new insights into ancient life in this rugged land.

“It’s a good baseline start,” Castañeda said, “but to looking more at how these different types of bedrock features played roles in hunter-gatherers’ lives, and looking at them in the context of their sites, will only bring us more answers.”