In 1964, when we were Peace Corps Volunteers in Nepal, we were invited to visit the King of Mustang in the ancient walled town of Lo Manthang on the Tibetan Plateau. To get there, we crossed the Himalayas on foot, climbing in and out of the deepest and steepest river gorge on earth, carved out by the Kali Gandaki as it flowed south between the Annapurna and Dhaulagiri mountain ranges. Our journey started in the terraced rice paddies around the hill villages of central Nepal, to coniferous forests on the steep southern slopes of the high Himalayas, and then to the arid, wind-eroded Tibetan...