Colorful thermal pool in the Fountain Paint Pot area of Yellowstone National Park - Photo by Frank Kovalchek

The Fountain Paint Pot is a mud pot located in Lower Geyser basin in Yellowstone National Park.
The Fountain Paint Pot is named for the reds, yellows and browns of the mud in this area. The differing colors are derived from oxidation states of the iron in the mud. As with all hot springs, the heat in the caldera forces pressurized water up through the ground, which is expelled here. Also, rising gasses cause the bubbling action. The bubble action in the mud varies with the seasons. In the early summer, the mud is watery from the high water table due to rain and snow melt. By the end of summer, the mud is much thicker as the water table drops.