Rainbow Bridge National Monument, 160 acres (65 hectares), S Utah; est. 1910. Rainbow Bridge, the largest natural bridge in the world, is a symmetrical, pink, sandstone arch, 309 ft (94 m) high, 33 ft (10 m) wide, with a 278-ft (85-m) span. Located in one of the most rugged and remote regions of the United States, it was discovered in 1909 by an expedition that set out to find the great stone arch rumored by the Native Americans. It is now accessible by boat from Lake Powell. See National Parks and Monuments (table).