The San Pedro runs not straight, wide, and deep, but twisting and turning in elegant oxbows, slow and shallow, as it offers its water to the lush grasslands, ci negas, and groves of trees that in turn stabilize its banks and shade its pools from the thirsty sun. Along its last miles in Mexico, the San Pedro, a foot deep and perhaps 20 feet wide in the early spring, more or less in other seasons, sustains the cattle of several ranches and waters many agricultural fields. Its banks bear the hoofprints of these unnatural but grateful users. Under a canopy of shimmering light and greenness, the San Pedro River slides quietly under a rusty barbed wire fence into the United States, accompanied only by the songs of vermilion flycatchers and yellow warblers, the piercing calls of killdeer and flickers, and the swift shadows of sharp-shinned and gray hawks. And I am struck by both the fragility and power of the green ribbon far below me in the center of the valley, the San Pedro River, a bright green tropical snake in a charcoal brown desert.
Water is the source of the power.
Along this green ribbon people have hunted and farmed and raised families for more than 13,000 years, from the prehistoric Clovis Culture who hunted mammoths and bison to the agricultural Hohokam and Sobaipuris, from the military and missionary Spaniards to modern-day industrial Americans. Yet if I squint slightly as I look down a thousand sloping feet to the river's snaking form, I can blur out the buildings and roads and see only a river flowing impossibly through a vast desert as it has for thousands and thousands of years. For millennia there have been people living in this valley, crowding close to the banks of the life-giving river like children clutching their mother's protective skirts, but their mark here is temporary in terms of the earth's clock, what we call geologic time. Nothing is constant, especially not the river. And it has writhed, and will continue to writhe, very much like a snake back and forth across the valley for many miles east or west, cutting down, down, down into its bed and then building up and up again.