Hot Springs

Hot Springs State Park covers approximately 1,087 acres in the town of Thermopolis in central Wyoming, centered around the world's largest single mineral hot spring, Big Spring. The spring produces over 3.6 million gallons of water per day at a temperature of 135 degrees Fahrenheit, flowing across a terraced travertine formation before entering the Bighorn River. The park offers free public soaking in the State Bath House, a tradition dating back to the original agreement with the Shoshone and Arapaho tribes, who stipulated that the springs should always be freely available to all people. A resident bison herd and the colorful travertine terraces add to the park's appeal.

The park maintains a small herd of bison on its grounds, providing visitors with reliable wildlife viewing. White-tailed and mule deer frequent the park. The Bighorn River through the park supports brown trout and rainbow trout fishing. Bald eagles and ospreys hunt along the river. Canada geese nest on the riverbanks. The warm spring water creates a unique microhabitat where thermophilic algae and bacteria thrive in the hot mineral water, creating the colorful deposits on the travertine terraces. Cliff swallows nest on the bluffs above the springs.

The park's vegetation reflects the semi-arid climate of the Bighorn Basin. Cottonwood and willow line the Bighorn River corridor. Sagebrush and native grasses cover the surrounding hillsides. The travertine terraces are largely devoid of vegetation, but the warm mineral water supports thermophilic cyanobacteria and algae that create vivid streaks of green, orange, and brown on the deposit surfaces. The park's maintained grounds include irrigated lawns and planted trees around the bath house and picnic areas. The surrounding hills display the typical dry grassland and sagebrush-steppe of central Wyoming.

Big Spring emerges from a deep geological circulation system where water percolates thousands of feet below the surface along fault zones in the Paleozoic-era Madison Limestone. The water is heated by the geothermal gradient and dissolved minerals including calcium, magnesium, sulfate, and chloride as it rises. Upon reaching the surface, the water cools and deposits travertine (calcium carbonate), building up terraced formations similar in principle to those at Mammoth Hot Springs in Yellowstone. The colorful terraces are constantly changing as mineral deposition creates new channels and surfaces. The spring's enormous flow rate makes it the world's largest single mineral hot spring.

Thermopolis sits in the Bighorn Basin at approximately 4,300 feet elevation, experiencing a semi-arid continental climate. Summers are warm, with temperatures in the 80s to 90s Fahrenheit. Winters are cold, with temperatures frequently below zero, but the hot springs create a naturally warm microenvironment. Annual precipitation averages only about 12 inches, making the area quite dry. Wind is common, especially in spring. The consistent temperature of the springs makes the bath house a year-round attraction, particularly enjoyable during cold winter days.

The hot springs have been used by indigenous peoples for centuries. The Shoshone and Arapaho tribes considered the springs to have healing properties. In 1896, the federal government negotiated the purchase of the springs from the Shoshone and Arapaho, who stipulated that a portion of the water must always be free for public use. This agreement led to the establishment of the free State Bath House, which continues the tradition today. The town of Thermopolis (from the Greek for 'hot city') grew around the springs, and the mineral waters attracted health-seekers in the early 1900s.

Hot Springs State Park was established in 1897, making it Wyoming's first state park. The original arrangement with the Shoshone and Arapaho tribes created the framework for the park's management, including the perpetual provision of free bathing facilities. The State Bath House was built in 1928 and has been renovated multiple times while maintaining its mission of providing free access to the mineral waters. The park's bison herd was established to provide an additional attraction and to preserve a piece of Wyoming's wildlife heritage. Commercial bath houses also operate in the park under concessionaire agreements.

The free State Bath House is the park's signature attraction, offering indoor and outdoor mineral hot spring pools at no charge. Commercial facilities including Star Plunge and Hellie's Tepee Pools offer waterslides and additional soaking options. The travertine terraces below Big Spring create a colorful, ever-changing geological display along walkways and overlooks. A short trail leads along the terraces and the Bighorn River. The bison pasture allows visitors to view the resident herd. A swinging bridge over the Bighorn River provides scenic views. The Wyoming Dinosaur Center is located nearby in Thermopolis.

The State Bath House provides free soaking in indoor and outdoor pools, with changing rooms and showers. Commercial bath houses offer additional pools, waterslides, and vapor caves for a fee. Picnic areas, walkways, and parking are available throughout the park. The park's campground (no hookups) provides basic camping. Thermopolis offers motels, restaurants, and services. The park is located on Highway 20 in Thermopolis, approximately 84 miles south of Cody and 130 miles west of Casper. The nearest commercial airports are in Cody and Casper.

Protecting the spring flow and mineral water quality is the park's primary conservation priority. The spring's source aquifer could potentially be affected by oil and gas development or other subsurface activities in the region. The travertine terraces are fragile geological features that can be damaged by foot traffic, and visitors are directed to stay on designated walkways. The park monitors spring temperature and chemistry to detect any changes in the geothermal system. Bison herd management includes health monitoring and population control. The park's commitment to free public bathing, honoring the original tribal agreement, requires ongoing maintenance and operational funding.