At approximately 1345 mountain time, a Cessna 310N was damaged during a hard landing at Glenwood Springs Municipal Airport and, at 1456, the airplane made a gear-up landing at Walker Field. The pilot and his passenger were not injured. The pilot said he made a hard landing at Glenwood Springs, followed by a go-around. Suspecting gear damage, he diverted to Rifle, Colo., but on his approach the right main landing gear fell off. Because of the limited emergency equipment in Rifle, he diverted to Walker Field. Witnesses confirmed the missing gear after he made a low pass over the runway, and the pilot retracted the gear and made an intentional gear-up landing.