The Sierra Madre Occidental of Mexico is wild, wild country. From the U.S. border south to Guadalajara -- over 500 miles -- only one passenger rail line and a single paved road cross those occult summits and tangled mazeways of gorge. The train route, between Ciudad Chihuahua and Topolobampo, is world famous for its scenery, and if the road isn't, it should be: 201 miles of dizzy, soaring blacktop, traversing high desert, pine forests, meadows, mountain ranges and jungle abysses.

The journey begins at Durango, a 17th-century ranching and mining metropolis that seems almost like an hallucination after the long, vacant drive down from the border -- a city famous for its mountain of nearly solid iron, and the lethal white scorpions who appear like an Old Testament plague during heat waves. It was William Burroughs who wrote, "In Mexico, your dreams have a special power." The first time I came to Durango, in the spring of '64, I had just seen a revival of "The Treasure of the Sierra Madre"; I met an American tramp prospector in the Plaza Principal who looked and talked exactly like Humphrey Bogart as the paranoid goldbug Fred Dobbs in the film. "I've been prospecting for gold," he said, gesturing up at the Sierra. "There's wildcats up there, and mountains so high the snow on top never melts." I still have no idea who or what he was: dream, ghost or elaborate joker. When we were through talking, he drove away in a very solid-looking Buick sedan, circa 1956.

From Durango, city of phantoms, you take Highway 40 west. The road climbs gradually, through pastures where thoroughbreds gallop, up the eastern escarpments of the Sierra Madre. The country changes: Arid grasslands give way to pine forests, meadows, scenes straight out of the Colorado Rockies. After 60 miles, you come to the ramshackle, rough-and-tumble mining town of El Salto, 6,685 feet above sea level. A few miles south lies the great canyon called Barranca de los Negros, on the upper reaches of the Rio Acaponeta. The country begins to open up around you.

Fifteen miles farther west, Highway 40 tops out at 9,000 feet. Clouds boil up out of the depths of the canyons; mists roll over the mountains, kindled by the arid air of the Great Mexican Desert striking the moist-subtropical atmosphere of the Pacific Coast. Gray stone gleams in the half-light. Men with flat brown Indian faces drive firewood-laden mules along the roadside; the fog swallows them up. Shacks perch on pinnacles, as unlikely-looking as those aerobatic huts in Chinese landscape scrolls. Locals say jaguars live in these mountains, and bears, and Indians of the Tepehuanes tribe, who let their fingernails grow until they are as long as swords; it is all probably true. But there are no snow-capped peaks: The ghost of Fred Dobbs dreamed those up.

Just past the village of La Ciudad, the road coils down a five-mile ridgeline called "The Devil's Backbone," with drop-offs of over a thousand feet on both sides. Parrots screech in the jungle canopy, far below. Through a break in the clouds, you can just see the Pacific, a nacreous gleam at the edge of the world. Past the massive and pompous monument commemorating the opening of the road in 1960, the parking lot ankle-deep in trash, garbage, debris; a few miles farther on, across the invisible line of the Tropic of Cancer. More vistas of mountain, cold and jade in the drizzle that is now falling; the Devil's Backbone, the spine of two continents. This is high, wild and lonesome country, from the Alaskan Arctic all the way down to Tierra del Fuego, the Land of Fire . . . mountains without end.

The descent, when it comes, is dramatic: a crash dive, down the steep western wall of the Sierra. Through precipitous jungles, past cornfields chiselled out of the hard slopes, tiny farms about to lose their balance and tumble into the Void; the air grows heavy, and sweet with flowers. You feel the same sense of anticipation you do in a big jet, coming in to land in a country you have never seen before.

The downslope runs out at last, and you are speeding west across the plains, near sea level now. Palm trees wobble in the orange dusk; ibises, their plumage glowing like white neon, tiptoe through darkening fields. Hit the main coastal highway at Villa Unio'n, and turn north: In a few minutes you are rolling into Mazatla'n, as the last clouds, lit by the drowned sun, burn out into red and golden ashes on the rim of the Pacific.