Climbing one of Colorado's 14,000-foot peaks used to be a solitary joy. These days 50,000 people top the state's famous "fourteeners' each year, and in one weekend on Mt. Harvard near Buena Vista, 133 signatures filled the summit register. Marketed in myriad guidebooks, the climbing craze is shattering solitude and trashing ecosystems, reports the American Mountain Foundation, based in Colorado Springs. The group says peak-baggers carve the hills with braided trails, and thrill-seekers run down alpine slopes "skiing the scree," causing slides of fragile talus rock. "There are those who are not in it for the wilderness experience," says Dave Duffy, an intern with the foundation. Duffy and five other interns studied 46 of 54 peaks this summer in cooperation with the Forest Service and three other outdoor groups. The participants, including the Colorado Mountain Club, Colorado Outward Bound School, and Volunteers for Outdoor Colorado, will recommend action to save mountains from too many people. Mary Beth Hennessy, outdoor recreation planner for the Forest Service in Leadville, says most of the crisscrossing "social trails' take off above treeline, where authorized trails become less distinct. For more information, contact the Colorado Fourteeners Initiative, American Mountain Foundation, 1520 Alamo Ave., Colorado Springs, CO 80907 (719/471-7736).