Mammoth Hot Springs was created over many millennia as hot spring water cooled and left deposits of calcium carbonate. The colorful runoff from the naturally white terraces is caused by bacteria and algae that thrive in the spring’s warm waters. All of this serves as a visible reminder of the deep volcanic and thermal forces at work in Yellowstone. To learn more, read informative plaques placed throughout the area. Mammoth Hot Springs is divided into Lower and Upper Terraces. Explore the Lower Terraces via a network of boardwalks. The boardwalks eventually connect to the Upper Terraces Loop, which you can also access by car.