The Last Barbarians:

In 1994, seizing the rarest of opportunities to journey deep into occupied Tibet, Michel Peissel accomplished what scores of Western explorers had tried and failed to do for more than a hundred years: He found the source of the Mekong River in the ice-strewn fields on the "roof of the world." This immensely readable account tells how a small group of modern adventurers made history not once, but twice, in the course of a single year: by accurately charting the origins of one of Asia's most majestic and storied waterways and by finding a living fossil, the Riwoche horse, a species unknown to contemporary zoology that may prove to be a missing link in equine evolution. The book's stage is forbidden Tibet - with its tragic politics, its natural wonder, and its fiercely independent nomadic tribes, who are known to the Chinese as "the last barbarians."