Across the river in the foreground, the Rainbow Terraces were formed by mineral deposits called travertine. The Big Spring produces 127° mineral water, and as the water moves down the terraces, changing temperatures and different colors of algae and micro-organisms give the terraces their multi-colored appearance. The site was sacred to several Native American tribes and was used for bathing and various ceremonies. Chief Washakie of the Shoshone and Chief Sharp Nose of the Arapahoe led the tribes in signing a treaty that gave the healing waters to the U.S. Government to be set aside for a National Park or Reserve and homesteads. Park facilities include group shelters, playgrounds, swimming pools, fountains, hotel accommodations, and picnic areas, and there is no entrance fee.