The Devils Hole spring, a unique desert Pupfish habitat is administered by Death Valley National Park, and located within the Ash Meadows National Wildlife Refuge, in Nye County, Nevada Southwestern United States.

Devils Hole' is a geothermal (92 °F/33 °C), aquifer-fed pool within a limestone cavern in the Amargosa Desert in the Amargosa Valley of Nevada, east over the Amargosa Range and Funeral Mountains from Death Valley.

Devils Hole branches into deep caverns at least 300 feet (91 m) deep from an opening at the surface that is approximately 6 by 18 feet (1.8 by 5.5 m). According to geologists, the caves were formed over 500,000 years ago.

Devils Hole is the only natural habitat of the Devil's Hole pupfish, which thrives in the hot water. It is an IUCN Red List endangered species.

en.wikipedia.org/wiki/Devil%27s_Hole

The Devil's Hole Pupfish is the smallest desert pupfish species in the Cyprinodon Genus.

Devil's Hole pupfish are less than 25 millimeters (1 in) long and resemble other pupfish in shape. They are the smallest of the desert pupfish species, averaging 19 millimetres (0.75 in) in length. They lack pelvic fins and have large heads and long anal fins. Breeding males are solid deep blue and have a black band on the caudal fin.

Devil's Hole pupfish have been the subject of considerable attention and litigation, due to their ancient origins, unusual habitat and precarious existence. A 22-thousand-year-old species, these pupfish depend on a shallowly submerged limestone shelf of only 2 metres (6.6 ft) by 4 metres (13 ft) in area for spawning as well as for much of their diet (primarily diatoms). Natural threats from flash floods to earthquakes have been known to disrupt this fragile ecosystem, but the major threat has been groundwater depletion due to agricultural irrigation.

en.wikipedia.org/wiki/Devil%27s_Hole_pupfish