On the morning of August 21—the day of the solar eclipse—five archaeologists and I piled into two SUVs and drove an hour northwest of Tucson, into the thick of the Sonoran Desert. Turning off-road, we reached a yellow expanse inside Ironwood Forest National Monument through a series of latched gates. We brought eclipse glasses, but the quarter-sliver of the sun was just a sideshow. Doug Gann, the archaeologist leading the trip, had brought us to the location of an ancient village—and he was going to fly a GoPro mounted on a drone over it.
The desert sun still seemed as blinding as ever, but not to his drone. Gann, who works at nonprofit Archaeology Southwest in Tucson, wanted to take advantage of the partial eclipse’s dimmer light to take better photographs: “You can see a little more detail in areas of shadow,” he explained later, after maneuvering the craft to take hundreds of overlapping aerial photographs.
But he wasn’t just trying to get pretty pictures. Later, in his office, Gann would process nearly 700 photos with software to produce a three-dimensional virtual model of the village where people known as the Hohokam once lived. The software calculates precisely the distance between every point in the picture using basic geometry and physics principles. “If you literally photograph the hell out of it, you can get incredibly accurate results,” says Gann. This technique of using photographs to create 3-D maps, known as photogrammetry, is about as old as photography itself. But archaeologists have only realized how they can use it in the last few years.
The landscape did not immediately brim with cultural significance. We hiked along a path of loose yellow dirt winding between nets of squat creosote bushes and prickly pear cactus. “Clear signs of overgrazing,” Gann commented, referring to industrial ranchers who used to raise cattle on the land. Several hundred years ago, when the Hohokam lived in the area, the place looked starkly different. “It was more of a grassland,” says archaeologist Aaron Wright of Archaeology Southwest. The Hohokam planted corn, beans, and squash using irrigation canals, and during the summer, they picked cactus fruit, such as the purple prickly pear. We picked them too, brushing the spines off on our shirts. They tasted mildly sweet of watermelon and were full of seeds.
As we hiked further, there it was: On the slope of a short hill, dark boulders piled up, etched with faded white shapes known as petroglyphs. Archaeologists squabble over the details, but they think the Hohokam carved the rock art between 600 and 1400 AD. Gann is mapping the hill so that he can eventually make a virtual reality exhibit for use in a museum or a classroom.