When I was 23, my best friend, John, and I decided to drive into Mexico. We had been on a ten-day trip around the United States, and Mexico looked like a tempting detour, so we got the required entry papers from a Texas notary who could barely type and headed south. We had a few hundred dollars between us and a hickory sledgehammer handle by the driver's seat in case we had to defend ourselves. We were going to Mexico at the height of the cocaine boom in the 1980s, and I now realize how ludicrous that idea was: Whatever problems waited for us down there were not going to be countered by a piece of hickory. I wasn't a journalist then, but looking back, that trip was the prototype for every frightening assignment I've ever taken.

Almost immediately a Mexican cop stopped us and, pocketing a five-dollar bribe, went on to tell us never to stop for anyone again down there—not even for other cops. There are bandits with fake police lights, he told us, and they'll pull you over and kill you for your money without a second thought. We continued on, wide-eyed.

We saw guys in street clothes with M16s and police checkpoints in the middle of nowhere and truckloads of federales careening through traffic with their automatic weapons at the ready. At one point we noticed a faint line in the scrub that crossed the desert like a surveyor's transect and seemed to lead toward a hill to the west. We got out of the car and followed it cross-country until we got to the top of the hill, and there we found ourselves at the intersection of two or three more lines that came dead-straight from the horizon and converged on a stone shrine about two feet high. Inside the shrine were bones.

That was Mexico—old and pagan and slightly ominous. John and I kept driving: Chihuahua, Delicias, Ciudad Camargo, Jiménez. The land was flat and dry and poor and seemed utterly without hope. By the time we approached Torreón, some 500 miles (805 kilometers) later, it was late at night and the Mex...