Thermopolis Hot Springs

Thermopolis is exceptional year-round, and the year-round nature of the hot spring makes it a genuine four-season destination. Winter (November through March) is arguably the most dramatic season — steam billows from the 127°F spring source in the cold air, coating the travertine terraces and surrounding trees with frost crystals; the contrast of the brilliant white steam clouds, the gold-and-white terraces, and the cold blue Wyoming sky is extraordinarily photogenic. Soaking in the free public pool at 104°F on a cold winter day is one of the finest experiences in Wyoming’s state-park system. Spring (April and May) brings higher Big Horn River flows (excellent for the trout fishery) and warming temperatures. Summer brings the highest visitor numbers (the water park and commercial pools are busiest) and the most comfortable temperatures for exploring the park on foot. Fall is excellent for the river fishing and the smaller crowds.

The hot springs at Thermopolis have been central to the culture of the Eastern Shoshone and Northern Arapaho peoples for centuries — the springs were considered sacred, a place of healing and spiritual renewal, and the treaty gathering that transferred them to Wyoming in 1896 was a solemn and significant event in the region’s history. Chief Washakie of the Eastern Shoshone negotiated the sale, insisting as a condition of the transfer that the state maintain a free public bathing facility accessible to all people in perpetuity — a condition Wyoming has honored for more than 125 years in the Big Horn Hot Springs free pool. The town of Thermopolis (Greek and Latin for “hot city”) grew as a resort community around the springs in the early 20th century, and the state park was established in 1916. The springs have been a destination for visitors seeking therapeutic mineral waters since the late 19th century, with the therapeutic reputation drawing visitors from across the American West.

Thermopolis Hot Springs is a thermophilic karst spring system — groundwater percolating deep into the earth through fractures in the underlying Wind River Canyon limestone sequence is heated by geothermal gradient (the natural increase in temperature with depth in the earth’s crust), picks up a rich mineral load (calcium carbonate, sodium, sulfate, potassium, bicarbonate, silica and trace minerals) from the limestone and dolomite it passes through, and rises under hydrostatic pressure to discharge at 127°F at the Big Horn River canyon rim. The enormous discharge rate (3.6 million gallons per day from the main spring) reflects the large recharge area of the Wind River Range and Owl Creek Mountains to the west and north, where snowmelt percolates into the karst system. The calcium carbonate in the water precipitates as travertine when the water reaches the surface and degasses CO2 — exactly the same process that creates Mammoth Hot Springs in Yellowstone — building the Rainbow Terrace and Teepee Fountain travertine mound formations over thousands of years.

Hot Springs State Park and the adjacent Big Horn River corridor support a rich and year-round wildlife community. American bison (a small herd maintained within the park as a historical-cultural element) are visible from the park roads year-round and are one of the park’s most popular attractions for visitors. White-tailed deer and mule deer are abundant in the riparian cottonwood forest along the Big Horn River. Bald eagles winter along the Big Horn River in significant numbers (the open tailwater below Boysen Dam remains unfrozen, concentrating trout and the eagles that prey on them — midwinter counts of 20+ bald eagles along the Big Horn River are common). Great blue herons, common mergansers, and belted kingfishers fish the clear river. The warm thermal area around the main spring supports unusual microorganism communities (thermophilic bacteria in the outflow channels) similar to those in Yellowstone’s thermal features.

The thermal spring ecosystem at Thermopolis is a unique microhabitat — the outflow channels from the main spring support communities of thermophilic (heat-loving) microorganisms, including cyanobacteria and other heat-tolerant algae that create the vivid yellow, orange, and green coloring in the outflow channels, analogous to the microbial mats of Yellowstone’s thermal features. The Big Horn River tailwater fishery below Boysen Dam is one of Wyoming’s most productive trout ecosystems — the cold, clear, nutrient-rich reservoir release supports exceptional brown and rainbow trout populations in the 15 miles of river between the dam and Thermopolis. The cottonwood riparian forest along the Big Horn River corridor is critical habitat for migrant and resident songbirds, raptors, and large mammals in the otherwise arid Wind River Basin.

Thermopolis Hot Springs occupies a unique place in Wyoming’s cultural heritage — a site sacred to the Eastern Shoshone and Arapaho peoples, the subject of a treaty negotiation that has been honored for more than 125 years, a Victorian-era resort destination that drew the wealthy and the ill-seeking-cure from across the American West, and today a genuine democratic public treasure (the free public soak guaranteed by Chief Washakie’s treaty condition is one of the most remarkable public-good legacies of any land-transfer agreement in the history of the American West). Wyoming takes justifiable pride in honoring that treaty commitment. The springs’ claim to being the largest mineral hot spring in the world is both scientifically validated and central to Thermopolis’s identity as a destination.

Thermopolis is in central Wyoming at the junction of US-20 and WY-120, approximately 85 miles south of Cody, 130 miles northwest of Casper, and 240 miles northwest of Cheyenne. Hot Springs State Park is immediately adjacent to the town of Thermopolis; the main spring and free bathing house are well-signed from US-20. Thermopolis has full services for a small Wyoming town (hotels, restaurants, the Wyoming Dinosaur Center). The park itself is free to enter; the commercial soaking facilities (Star Plunge, Hellie’s Tepee) charge modest admission. The Wyoming Dinosaur Center charges a separate admission. No reservations are needed for the free public bathing house. Check Wyoming State Parks for current hours of the state-operated facilities.

Wyoming State Parks manages Hot Springs State Park. The travertine terrace formations — the Rainbow Terrace and Teepee Fountain — are fragile calcium-carbonate structures built up over thousands of years; do not walk on the travertine or touch the formation surfaces (body oils and physical contact damage the delicate mineral crust). Stay on designated walkways around the spring mound. The free public bathing house is a state-maintained facility; treat it with respect. The bison herd is maintained as a managed wildlife exhibit; do not approach or feed the bison (they are wild animals capable of serious harm). Support the Wyoming Dinosaur Center’s active paleontological field program, which contributes to the region’s scientific heritage.

The spring water discharges at 127°F — do not enter any outflow channel or unmanaged spring water (the temperature is capable of causing severe burns instantly). The public and commercial soaking pools are maintained at safe soaking temperatures (100–104°F) by diluting the spring water. Pregnant women, people with cardiovascular conditions, and those on certain medications should consult a physician before soaking in mineral hot springs (the heat and mineral concentration can have significant physiological effects). Bison in the park are wild animals — maintain a minimum distance of 25 yards and never approach or feed them. The Big Horn River below the park can rise rapidly after upstream reservoir releases; check current conditions before wading to fish.

Hot Springs State Park is free to enter. The free public Big Horn Hot Springs bathing house is open daily (check Wyoming State Parks for current hours). Commercial soaking facilities (Star Plunge, Hellie’s Tepee) charge separate admissions. No climbing on or touching the travertine formations. Bison viewing from a minimum 25-yard distance; never feed bison. Big Horn River fishing requires a Wyoming fishing license. Wyoming Dinosaur Center charges separate admission and dig-site tour fees. No camping within Hot Springs State Park (campgrounds available at nearby state facilities). Pack out all trash.

The Wyoming Dinosaur Center in Thermopolis (one of the finest dinosaur museums in Wyoming, with active Jurassic Morrison Formation dig sites accessible on guided tours — an extraordinary addition to any Thermopolis visit), Wind River Canyon (15 miles south on US-20 — a spectacular 2,500-foot-deep canyon where the Wind River cuts through the Owl Creek Mountains, exposing billion-year-old Precambrian rock; one of Wyoming’s most dramatic scenic drives), Boysen State Park (15 miles south — Boysen Reservoir with boating, camping, and excellent walleye fishing), Cody (85 miles north via US-20 — the Buffalo Bill Center of the West — one of the finest museum complexes in the American West), and the Big Horn Basin define the region. Thermopolis makes an excellent overnight stop on any cross-Wyoming itinerary.

Visit the free Big Horn Hot Springs bathing house first thing in the morning (it opens early and is least crowded before 9 AM) for the finest soaking experience — the free pool is covered but open to the cool morning air, and the combination of 104°F mineral water and cool Wyoming morning sky is deeply restorative. Drive or walk to the Rainbow Terrace immediately after soaking — the morning light on the gold-and-white travertine cascade, with the steam rising from the main spring source, is exceptionally photogenic. If visiting in winter, time your visit for a clear cold day — the steam plumes from the 127°F main spring, backlit by the low-angle winter sun, create extraordinary photographic opportunities. Plan a half-day at the Wyoming Dinosaur Center; the active dig-site tour (where you may observe or participate in actual Jurassic fossil excavation) is one of the most distinctive outdoor experiences in Wyoming.