Indian leaders, former astronauts and other visitors stepped gingerly beyond the Grand Canyon's rim, staring through a glass floor and into the 4,000-foot (1,219-meter) chasm below during the opening ceremony for a new observation deck. A few members of the Hualapai Indian Tribe, which allowed the Grand Canyon Skywalk to be built, hopped up and down on the horseshoe-shaped structure. At its edge - 70 feet (21 meters) beyond the rim - the group peeked over the glass wall. "I can hear the glass cracking!" Hualapai Chairman Charlie Vaughn said playfully. The massive deck is anchored deep into a limestone cliff. As people walk across it, the glass layers creak and the deck wobbles almost imperceptibly. To one side, the Colorado river appears as a slim, pea-green ribbon. Former astronaut Buzz Aldrin, who was invited to visit, declared it a "magnificent first walk."