Mammoth Cave, Lava tube in Garfield County, United States.

Mammoth Cave is a lava tube on the Markagunt Plateau in Dixie National Forest, Garfield County, Utah. It has four chambers, the largest to the west, and over 2,200 feet (670 m) of passage in a system about a quarter mile (400 m) long. At the end of the largest tunnel it narrows to a small opening that can be used as an exit.

The cave formed less than 2000 years ago when lava cooled and water flowed through the rock, carving out these underground voids. This process shaped the various chambers and passages visible today over that relatively short geological timespan.

During winter months from October to April, sections of the cave remain closed to protect the native bat populations during their hibernation period.

Visitors should bring multiple light sources and wear sturdy footwear, as floors are rocky and become muddy in sections. Navigation in darkness requires caution and proper preparation before entering the system.

The cave has four chambers, the largest lying to the west. At the end of the longest tunnel the passage narrows to a small opening that can serve as an exit, so the route through the lava tube does not simply end in a wall.