Mammoth Paint Pots is a historic name that was changed (probably to reduce geographic confusion). Today they are named Fountain Paint Pots. They were orginally named "Mud Puff" by the 1871 Hayden Survey. They are located midway between in the Midway and Lower geyser basins (about half way between Old Faithful and Madison).
The mud is composed of clay and silica formed from the breakdown of volcanic-derived sediment and spring deposits. In "real colors" the mud ranges from yellows, reds, and browns from differing oxidation states of iron in the mud. The bubbling results from escaping gases: steam, carbon dioxide, hydrogen sulfide, and traces of other gases.