They call Chaco Canyon in New Mexico the Stonehenge of America and its nine magnificent pueblos "great houses." The greatest of them all is Pueblo Bonito, built during the eighth to 11th centuries A.D. Semicircular, three stories high, with two large plazas and numerous subterranean chambers, this stupendous pueblo is one of the great architectural wonders of ancient America.
Places like Chaco Canyon make journeys in search of the past profoundly worth it in a world where so much archaeology is very specialized, often narrow and, frankly, sometimes rather dull. At Chaco even the casual visitor can explore new things for days. But as you visit the great houses, you also see the impact of drought on our world.
We've known about the Chaco droughts for years, but it's only recently that we've learned just how widespread droughts were in the American West of a thousand years ago. The great Chaco drought coincided with long dry cycles in California, which provide sobering food for thought today as California experiences another year of drought. Scott Stine, a geography professor from California State University, Hayward, has studied the rings of trees that once grew on the lakebed of Owens Lake on the eastern flanks of the Sierra Nevada. He found evidence of seven droughts between A.D. 900 and 1250. In 1025, the lake level was more than 130 feet below today's shoreline.
Stone extended his research to other lakes such as Mono Lake, the northernmost catchment of the Los Angeles aqueduct. He found more evidence of prolonged dry cycles, one that lasted for about 190 years, from 910 until about 1100, and a second that lasted nearly 140 years, that began before 1210 and ended in about 1350. The same droughts extended as far north as east-central Oregon and into the Rockies and adjacent Great Plains.
Chaco Canyon lies at the mercy of the irregular rainfall of the San Juan Basin encompassing northwestern New Mexico. Why, then, did the Ancestral Pueblo build elaborate great houses here? The canyon itself could only support about 2,200 people, certainly not enough people to build the pueblos by themselves. There was something compelling about Chaco that attracted villagers from miles around. Generations of Ancestral Pueblo flocked here for major ceremonies, perhaps to commemorate the passage of the solstices. They carried in 200,000 tree trunks from as far as 50 miles away to serve as beams for the great houses.
Thanks to ancient tree rings, we have such accurate pictures of long-forgotten droughts that we can track arid cycles as they moved across the Southwest centuries ago. The zigzag growth patterns in Chaco's tree rings are a sobering chronicle of persistent droughts, which culminated around 1100 in a 50-year dry spell. Chaco emptied rapidly. Family by family, the permanent residents of the great houses moved away, to live with kin where water was more abundant.
The droughts occurred because the winter jet stream over the northeastern Pacific and its associated storm tracks stayed well north of California. After 1300, there was an abrupt change to persistently wetter conditions, which lasted for 600 years, before giving way to today's arid conditions. None of today's droughts approach the intensity and duration of the epochal dry spells of a thousand years ago. These prolonged droughts occurred because of warming throughout the world and persistent, dry La Niña conditions in the Pacific. The lesson is clear: Even modest warming can bring serious drought to California.
We are now living though a warming cycle that began about 1860 and continues unabated. The incidence of drought has risen 25 percent worldwide since 1990. Britain's Hadley Meteorological Institute is one of several institutions that have developed sophisticated, and frightening, computer models of the effects of continued warming. By 2100, extreme drought will affect a third of the world's surface, up from 3 percent. Moderate drought will descend on half the world, a doubling from today. The aridity will hit hardest in arid and semi-arid lands, among them the American West and tropical Africa, where self-sustainable agriculture is chancy even with plentiful rainfall. With our promiscuous urban development and industrial-scale agriculture (70 percent of California's water goes to farming), we have already strayed far from any form of self-sustainability.
I recently visited Phoenix, where unbridled urban sprawl rules and the population is exploding, despite rapidly diminishing water supplies. While the experts worry, the public at large seems little interested in serious, collective efforts at water conservation. Here in California, too, we live in a state of comfortable denial. You can hardly blame us, residing as we do in an environment of short-term thinking where we are accustomed to instant self-gratification. We turn on faucets and water is there, however dry the landscape outside the kitchen. The thought of a 140-year drought is almost beyond comprehension, yet we may well be entering one. To deny the possibility, to suggest that history is no guide, is just plain stupid.
Whether we like it or not, droughts and water define our lives. Water shortages are on the horizon now. If the Hadley's projections are correct, they'll be a daily reality in our great-grandchildren's time, unless we become really serious about water conservation as a society. That's the lesson of Chaco's silent great houses, where people conserved water rigorously, yet were defeated by prolonged drought.
It takes serious commitment and long-term thinking to develop water conservation that works for the benefit of future generations. And part of this effort must include education about water issues from the earliest age, for conservation is, after all, a social problem as well as a practical one. But, as Chaco hints, this is something that needs to transcend petty concerns about tax increases and ideological fixations. It's a matter of the collective survival of the West as we know and love it.
Brian Fagan is Emeritus Professor of Anthropology at the University of California, Santa Barbara, and the author of "The Great Warming: Climate Change and the Rise and Fall of Civilizations." The Sacramento Archeological Society will present a lecture by Fagan at California State University, Sacramento, on Saturday. Go to www.sacarcheology.org.
