Beyond human and animal migrations across the U.S.-Mexico border, another process is continuously active: the movement of groundwater.
The Gran Desierto region of the Sonoran Desert is the largest area of sand dunes in North America.
On your way south to Puerto Peñasco (or Rocky Point), the large dune field to your right is what used to be the interior of the Grand Canyon, brought to rest here by the once-mighty Colorado River.
North of Peñasco, the arid Sonoran coast of the Gulf of California is filled with sands that seem to extend endlessly until they abruptly meet the sea.
However, nestled into these dunes along the coast is a series of salt flats from which an array of freshwater springs, or pozos, seems to magically appear.
This is the only fresh water for at least 50 kilometers in any direction and was the destination for centuries of old salt pilgrimages by the Tohono O’odham.
Where does this water come from and how old is it?
A transdisciplinary collaboration among a botanist, a hydrologist and an artist seeks to answer these questions.
Beyond academic papers, as part of the Next Generation Sonoran Desert Researchers 6&6 art-science collaboration (nextgensd6and6.com) results of the work will be shown at the University of Arizona Museum of Art January-April 2019.
After nearly two years and over a dozen trips, a cohesive story of permanence has emerged.
Water samples analyzed for stable isotopes — chemical signatures of elements in the water itself that tell where and when the water is from — reveal that this water is ancient, deposited toward the end of the last Ice Age, about 10,000 years ago.
Its origin seems to share a history with the former paths of the Colorado and Gila rivers.
Thousands of camera-trap images show a riparian habitat at the center of life for multiple species, especially coyotes, great blue herons, migrating water fowl and bats in the summer.
A myriad of archaeological remains fills the dunes at the edges of the springs, which contrast with the continuous hum of traffic along the new coastal highway that offers a shorter route from California to Sonora.
Freshwater springs that used to be a sacred destination are now bypassed unknowingly as thirsty cities continue to grow.
This hidden water once used over millennia by desert peoples and still essential to animals in the dune fields is central to the larger story of how humanity interacts with water in the binational Sonoran Desert.