“I LOVE ALL THINGS that flow,” said James Joyce. “If there is magic on this earth it lies in water,” Loren Eiseley said. And nowhere is water so beautiful as in the desert, for nowhere else is it so scarce. By definition. Water, like a human being or a tree or a bird or a song, gains value by rarity, singularity, isolation. In a humid climate, water is common. In the desert each drop is precious.

Way down in a corner of Arizona, near the Mexican border, is a tiny spring called Sweet Water. This spring is the only permanent, reliable, natural source of water between Quitobaquito on the east and the Tinajas Altas (“High Tanks”) on the west—a distance of sixty miles by road. That road, surfaced in sand alternating with long stretches of blue-black lava rock, was called the Vulture’s Road. Long since abandoned, bypassed by paved highways far to the north and south, the Vulture’s Road can still be followed here and there, the route identifiable by dim tracks across the stone, by cast-off wagon-wheel rims and antique Ford mufflers dissolving in rust and by the mounds of stones and iron crosses that mark the burial sites of those who never made it. No one with any brains ever traveled that road in summer. In winter the low desert can be comfortable, even exhilarating, if you’re properly equipped for survival; but in summer it is intolerable. The shimmer of heat waves, hanging like a scrim across the horizon, is enough in itself to confuse the senses, puzzle the mind. The mountains float like ships on the waves of superheated air, drifting away from one another, then returning, merging, inverting themselves, assuming shapes out of fantasy. The madness of mirage.

Some of those passing on that road must have wondered, as they endured the heat and the thirst, what lay within the folds of a certain small mountain range to the north. A typical desert range: blue hills prickly with cactus, agave, spiny shrubs and stinging nettles, mostly bare of any vegetation at all, scaled and plated with loose rock, the high ridges notched with points like a dragon’s backbone. What a few men knew was that there was water in there—the spring of Sweet Water. Not that the knowledge would have done the travelers much good. The spring is far from the road, difficult to reach; the effort required to get there might have taken more lives than the little trickle of water could have saved. In the desert it is usually more important to ration bodily energy than water itself; sweat may be as costly as blood.

One morning in March I drove my government truck into the area, through the cactus forest to the end of the dim track, then walked the last few miles. I had plenty of water with me and within me; I was being paid to patrol these parts, investigate worked-out gold mines, check game trails, inspect animal droppings, test the water of hidden tanks and secret springs.