A Lost Civilization May Shed Light on Coping with Climate Change
An innovative collaboration between scientists is discovering how, 700 years ago, a mysterious, prehistoric culture overcame its landscape's harsh constraints. The findings may tell a cautionary tale for today's Southwest.
Until recently, scientists familiar with the archaeological sites had speculated that the former inhabitants moved to Perry Mesa out of desperation. A drought lasting decades rocked much of the Southwest in the 1200s, setting off a fierce scramble for dwindling food resources. During this dark period, many populations moved away from valleys to upland areas, where larger groups clustered together in defensive-oriented settings. The most famous example--still widely debated--is that of the Anasazi, a sophisticated culture in the Four Corners area that had built an impressive network of farming villages over hundreds of years before abandoning them, beginning in the mid-1200s, for precarious cliff-top dwellings.
The case of Perry Mesa is no less befuddling, if not nearly as well known. When I visited there last spring, I had a hard time imagining how anyone could survive the harsh conditions for a month, much less decades. The 75-square-mile tract has a post-apocalyptic, Planet of the Apes aura. Wind whips constantly. Walking is arduous; the terrain, uplifted atop a bed of volcanic rock, is strewn with broken boulders. Thick masses of thorny mesquite and prickly pear cactus hug the brownish ground, which also sprouts patches of frail tobosa grass.
When Hoski Schaafsma starts describing the ancient gardens that once blanketed the landscape, I stare at the dirt in disbelief. All I can make out is a gray, rocky jumble. But Schaafsma, a pony-tailed ASU plant biologist, has in the past few years decoded an astonishing pattern of land use atop Perry Mesa. "This whole hillside is terraced," he says, sweeping his arm across a lumpy area of the mesa. "What we're standing on here, this sort of linear clump of rocks, is drainage, where they were catching the water and soils for agricultural purposes." What appears, at first blush, to be a random assortment of large stones are actually the remnants of an intricate network of irrigation and cultivated farm fields.
Seven centuries ago rocks were moved and positioned in a way to create walls perpendicular to a given slope so that they caught water and soil after monsoonal rains. Some of the surface soil at Perry Mesa is sandy, which is not the best for farming. But the manipulation of rocks into a series of walls that form terraces engineered a loam for maximum agricultural productivity.
The people of Perry Mesa thus teased corn, beans, and agave from a marginal environment--relying only on rainwater. The technique, known as dry farming, was perfected by prehistoric Indians in the hot, arid Southwest. But the extent to which it was practiced seven centuries ago on this bleak terrain has proven revelatory.
Even seasoned archaeologists who have spent years studying Perry Mesa admit to being surprised by the vast agricultural footprint. "If you walk across the landscape and all you're looking for is stone houses, then that's all you'll find," says Schaafsma, who had an archaeology background before expanding his portfolio with academic training in ecology. To date, he and his colleagues have documented about 1,000 terraces, with many more expected. As Rem Hawes, manager of Agua Fria National Monument, puts it, Perry Mesa's "entire landscape was intensively managed to control and collect water, grow crops, and support a thriving society."
In doing so the indigenous inhabitants--whose descendants are thought by some to be the Hopi, a tribe that still practices dry farming in northern Arizona--totally changed the composition of the soil and altered the plant community, a legacy that continues today. "These people [on Perry Mesa] essentially created their own unique ecosystem," marvels Connie Stone, a BLM archaeologist who advises on the management of the monument.
How a prehistoric culture transformed this inhospitable environment is just becoming clear, but the most obvious questions still mystify scientists. "Why did they move up there, and why did they leave?" asks Jeffery Clark, an archaeologist with the Tucson-based Center for Desert Archaeology.
An even bigger mystery ties archaeologists in knots. Seven hundred years ago long-established prehistoric cultures started collapsing across the Southwest. The region had been booming for centuries, abetted by the spread of agriculture and complex trading networks. Then, about 1350, the Anasazi disappeared from the Four Corners region. At the same time the rugged Fremont people, dispersed in semi-subterranean pit-house villages in Utah, also vanished from the archaeological record. The chaotic upheaval extended from what's now Salt Lake City to southern Arizona and into Mexico for another 200 years. By the 1400s the highly organized Hohokam, which had built extensive irrigation canals in the Phoenix area, collapsed, punctuating the grim span.
The debate over what happened to all of these people has been notoriously contentious for decades; researchers have pointed variously to drought, warfare, or, lately, a mass exodus to areas where the landscape could better support farming. Perry Mesa appears to have been among the best of the worst places. Recent tree-ring analysis by one of the ASU researchers, Scott Ingram, points to a wetter period in central Arizona during the 1300s, when the pueblos atop Perry Mesa expanded, supporting as many as 1,000 people. It's possible they came out of desperation in the late 1200s but then used their ingenuity and an improving climate in the 1300s to set down roots. "I can understand why people would live there at this time, but what I don't understand is the configuration of the houses," he says, referring to their placement along canyon rims.