Six years ago I learned an important lesson about mountains and weather--from a farmer's horse. I was studying the geology of the ancient Kingdom of Mustang, now part of Nepal. Mustang lies high on the edge of the Tibetan Plateau, at the headwaters of the remarkable Kali Gandaki River, which carves a deep valley between the 8,000-meter-high peaks of Annapurna I and Dhaulagiri as it descends south to the Himalayan foothills. The farmer told me that the horse was perfectly good anytime for riding around on the plateau. But he mysteriously warned that if I were riding into the valley the horse would be good only in the morning.

I didn't understand his meaning until just after noon, when in a narrow part of the valley the horse and I found ourselves facing into a gale-force wind that seemed to come out of nowhere. As the winds intensified, the horse went slower and slower until it finally stopped, shook its head and turned around. No amount of prodding would get it to head into the wind with me on its back. As I dismounted and dragged it to the valley by its bridle, the thought occurred to me that this horse might know more about the weather patterns of the Himalaya than I did.