The Fountain Paint Pots are one of the biggest attractions of the Lower Geyser Basin at Yellowstone National Park. In this huge pit, an acidic mud composed of clay and silica particles boils away under the influence of geothermal heat. The color, which ranges from gray to pink, comes from minerals in the original rock that formed the mud.

The nature of the pots changes over the course of the year. In the spring, higher water content causes the mud to be liquid and so it boils almost like a thick soup. Over the summer the pots dry out and begin to form cracked, dry formations as you can see on the edges of the pots here.