The other side of the border was like a Fellini film in sombreros. The narrow street was lined with dental offices, cut-rate surgeries, and offices of plastic surgeons. A young man in green scrubs – he could have been some sort of official – waved us to the curb. Dupes that we are, we pulled over. When he asked which medical specialty we were seeking, we realized our mistake, pulled out, and headed as fast as permissible – Mexican roads are studded with speed bumps – for Mexicali.

Travel, the old adage goes, is broadening and educational. It can also make you feel like an utter rube. My memories of the Southwest and Mexico were 60 years old, and utterly failed to prepare me for the countless square miles of looping, entwined concrete highway overpasses, car dealers, and hotels of Phoenix. Likewise Mexicali, which I envisioned as an updated, flat-roofed adobe village. Wrong again. The metropolitan area is home to almost a million people, most of whom drive like hell and, unlike us, know where they’re going. But the hotel was pleasant enough, with a pool, gym, free-drink receptions, and two-for-one happy hours on alternate evenings. Once again, luxuriating in a single room, I tested my conviction that the most dangerous spot in any hotel is the shower – with the predictable results.

The day before our drive to Mexicali I’d spent in a Cessna 172 with an elderly private pilot who volunteers for an organization named Lighthawk, which serves as a magic carpet and eyes in the sky for various conservation groups. Last October we flew with them as they helped track California condors in the mountains behind the Big Sur. This time we were filming the slow disappearance of the Colorado River as it bleeds its precious water right and left to support the activities of 30 million people along its length, as well as the agriculture of California’s Imperial Valley.

Our pilot, Will Worthington, had been an engineer who’d worked on several of the dams in his younger days, and now, in an act of contrition, was doing what best he could to mitigate their effects. “We considered every possible ramification of our actions and designs,” he said, “except one: the effect on the downstream environment.” The Colorado is a desert river; when it has no water, nobody near it has water. We flew over the Grand Canyon, roaring with energy, and slowly worked our way south, landing for lunch on the Nevada border, with casino hotels looming just across an impoundment. After lunch we traced the slowly diminishing river past green farm fields, canals, pipelines, and riverside marinas and vacation homes. You could see how planners could miss the ultimate result of all the subtractions.

We saw them next day. Driving south from Mexicali past miles and miles of concrete-block shacks with tarpaulin doors, junk yards scandalized for all salable parts, and tired-looking palm trees, we reached a tiny museum and gift shop beside the highway where the indigenous Cucupá people, who lived sustainably here for at least a millennium when the river still flowed, eke out a living. Sitting on a bench in front of the museum with Inocencia, an 82-year-old Cucupá and her very friendly mutt, Noblé, I asked, through an interpreter, about the days of the river. Oh, yes! she remembered. We women had a fishing club, and we caught lots of fish in Laguna Grande.Then the laguna dried up, and so did the club. She shook her head when I asked if she thought the water would ever come back. She seemed past regretting its loss. Her daughter, an activist, was more sanguine. The recent decision by Mexicali to treat its effluent and feed it back into the lower Colorado system promises some running water in the delta before much longer.

We drove next day in a caravan of conservation-minded philanthropists to the dedication of a new interpretative center of the Sonoran Institute. Headquartered in Tucson, the institute is dedicated to the restoration of the desert Southwest. Inocencia’s daughter and four Cucupá kids blessed the building with incense and a dance, there were speeches, and a lovely taco lunch alfresco.

The land around the center was composed of the finest silt– every step sent up a puff of dust – full of tiny freshwater clam shells. Local families came to a large, completely barren field to plant several hundred saplings in holes that will be irrigated from a nearby slough. The field will be a jungle again in ten years. And the locals, in the best possible way, will be invested in the recovery of their once-fertile delta.