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Thermopolis Hot Springs
Hell's Half Acre
Discover the Geology of the Thermopolis Hot Springs
A great way to relax while traveling across Wyoming is a soak in the mineral
hot springs in Thermopolis. Hot Springs State Park was established in 1937 to protect mineral springs that produce nearly 3,000 gallons per
minute of water at a temperature of more than 130˚F. The bubbling action in the springs at
Thermopolis is caused by carbon dioxide and hydrogen sulfide gas. Hot Springs
State Park contains two commercial pools and a state-run Bath House. There are
many private springs and wells associated with the same geothermal system north of the park.
The springs emerge from the crest of the Thermopolis anticline, which is a
large geologic fold that formed during the Laramide orogeny (70–35 million years ago). The Laramide mountain-building
event faulted and folded the red Triassic-age rock layers seen around the hot springs, and the
hot water is thought to be traveling up to the surface along those faults.
Big Spring is the largest of the park’s springs, with hot water flowing across an impressive system of
terraced travertine down to the Bighorn River. Travertine forms by precipitation of carbonate minerals from hot
water, and builds up over time forming terraced steps. The bright colors are caused by the incorporation of thermophilic
organisms like bacteria and algae into the travertine. Extensive travertine, sulphur, and gypsum deposits mostly west of the river
indicate hydrothermal activity has not always been confined to its present location.
The Traveler's Guide to the Geology of Wyoming explains how a thermal springs may form, and
a WSGS preliminary report details the Thermopolis hydrothermal system.
Additional information about the hot springs at Thermopolis can be found on the following websites:
Wyoming State Parks
Blackstone, D.L., Jr., 1988, Traveler’s guide to the geology of Wyoming (2d ed.):
Geological Survey of Wyoming [Wyoming State Geological Survey] Bulletin 67, 130 p., 13 pls.
Fountain of Youth RV Park, 2017, Hot springs pool at Fountain of Youth RV Park, accessed February 2017,
Lageson, D.R., and Spearing, D.R., 1988, Roadside geology of Wyoming (2d ed.): Missoula, Mont., Mountain Press Publishing Company, 253 p.
Hinckley, B.S., Heasler, H.P., and King, J.K., 1982, The Thermopolis hydrothermal system, with an analysis of Hot Springs State Park:
The Geological Survey of Wyoming [Wyoming State Geological Survey] Preliminary Report 20, 42 p., 1 pl.
Wyoming State Geological Survey, 2017, Geothermal uses, accessed February 2017 at, http://www.wsgs.wyo.gov/energy/geothermal.
Christina George (307) 766-2286 Ext. 231