The Rainbow Terraces in Hot Springs State Park are formed by springs that discharge more than 3 million gallons of 135-degree-Fahrenheit water laden with minerals every day, making them the largest such mineral hot springs in the world. This is the primary trail in the park that highlights all of the main pools and terraces. You'll get to see many vibrant colors from the algae that feed on the minerals in the 135-degree water. The colorful travertine terraces built from millions of years of mineral build-up are reminiscent of the Mammoth Springs in Yellowstone, but quite a bit smaller. The western and northern half of this loop trail are made from slightly elevated boardwalks that take you through the springs. The eastern half of the trail is paved.