Calhoun began her career in mountain climbing as an Outward Bound guide in Colorado after graduating from college. She later became a guide for the American Alpine Institute, with whom she led climbs in Peru, Bolivia, Alaska, Argentina, and Nepal. On a personal trip to Peru in 1984, she climbed Pirámide, Alpamayo and Qitarahu. In 1987 she was the first American woman to climb Dhaulagiri in Nepal, marking her first 8,000-meter peak, although she and her teammates had no Himalayan climbing experience. She subsequently received invitations to climb Mount Everest and join other high-profile expeditions, but she opted instead to lead her own expeditions with close friends. In recognition of her second 8,000-meter summit—an expedition she led up Makalu's highly technical West Pillar route—she was awarded the Robert and Miriam Underhill Award, the highest honor given by the American Alpine Club. She was the first woman to climb Makalu, the world's fifth-highest mountain.