The vestigial cobblestone path lasts only 50 feet, climbs a set of broken stairs, then once again disappears, swept away by years of monsoonal deluges. I carry on, entering a narrow passage where the sidewalls are so steep and slippery I have to hang on to trees to keep from falling into the bouldery creek far below. I'm hoping, at some point, to cross over Maan Shan, a high pass between Yaan and Kangding.

That night I camp high above the creek, but the wood is too wet to make a fire. Rain pounds the tent. In the morning I probe ahead another 500 yards before an impenetrable wall of jungle stops me, for good. I'm forced to admit that here at least the Tea Horse Road has vanished.

In fact, most of the original Tea Horse Road is gone. Recklessly rushing to modernity, China has been paving over its past as fast as possible. Before the trail is bulldozed or obliterated, I've come to explore what's left of this once famous but now all-but-forgotten route.

The ancient passageway once stretched almost 1,400 miles across the chest of Cathay, from Yaan, in the tea-growing region of Sichuan Province, to Lhasa, the almost 12,000-foot-high capital of Tibet. One of the highest, harshest trails in Asia, it marched up out of China's verdant valleys, traversed the wind-stripped, snow-scoured Tibetan Plateau, forded the freezing Yangtze, Mekong, and Salween Rivers, sliced into the mysterious Nyainqentanglha Mountains, ascended four deadly 17,000-foot passes, and finally dropped into the holy Tibetan city.

Snowstorms often buried the western part of the trail, and torrential rains ravaged the eastern portion. Bandits were a constant threat. Yet the trail was heavily used for centuries, even though the cultures at either end at times despised each other (and still do). The desire to trade was why the trail existed, not the romantic swapping of ideas and ethics, culture and creativity associated with the legendary Silk Road to the north. China had something Tibet wanted: tea. Tibet had something China desperately needed: horses.

Today the trail lives on in the memories of men like Luo Yong Fu, a watery-eyed 92-year-old whom I met in the village of Changheba, a ten-day walk for a tea porter west of Yaan. When I first arrived in Sichuan, I was told no tea porters were still alive. But as I walked the last remnants of the Chamagudao, the Chinese name for the ancient trade route, I met not only Luo, but also five others, all eager to share their stories. Stooped but still surprisingly strong, Luo Yong Fu wore a black beret and a blue Mao jacket with a pipe in the pocket. He had worked on the Tea Horse Road as a porter, carrying tea to Tibet from 1935 to 1949. Luo's load of tea always weighed 135 pounds or more. At the time, he weighed less than 113 pounds.