Known today as the Thumb Paint Pots, the Hayden Expedition of 1871 originally named these fanciful features the "Mud Puffs." Picture a field of miniature mud volcanoes that are 3 to 4 feet (1 meter) high with steam curling from their delicate mud chimneys in various shades of red. Surrounding the cones, the mud appears to be stirred and mixed to the smoothest, most satiny consistency by some unseen hand. Mud pots vary with precipitation and groundwater levels. Sometimes they look like muddy water; other times they look as if you could build pottery with their mud.