World's Largest Mineral Hot Spring
Hot Springs State Park Loop Road

History: These springs were included in the Shoshone Indian Reservation created by the Treaty of 1868. Later the reservation was also used for the Arapahoes. As information that the springs have “magnitude, health giving properties” became more generally known, Congress was requested to set aside this area for a “National Park or Reservation.” In 1896 upon authority from Congress, the Indian Commissioner sent John McLaughlin to negotiate a treaty for the purchase of these springs. He secured an agreement whereby a part of the reservation, approximately 10 miles square was ceded to the United States Government for the sum of $60,000.00. Among the signers of this treaty were the Shoshone Chief Washakie and the Arapahoe Chief Sharp Nose. Chief Washakie said that when game was bountiful in this area, he used to camp near the spring. But by 1890 hunting was so poor in this vicinity that it was seldom visited by the Indian.

Geology: Most of the water in these springs is thought to come underground from the Owl Creek Mountains. Rain falling in the mountains enters porous rock layers, moves slowly downward, and is here forced through crevices in the rocks.
The heat and chemicals in the water are derived from the rock through which it passes and from gases that rise from deeply buried volcanic rocks.

The terraces are made chiefly of lime and gypsum which separate from the cooling water. The colors are due mainly to primitive plants (algae) which grow in the warm water.

Chemistry:
Minerals Chemical Composition Parts per million
Silica SI O2 24.0
Aluminum AL2O3 11.6
Iron FE2O3 14.8
Calcium CA0 624.0
Magnesium MGO 121.0
Sodium NA20 326.2
Potassium K20 89.6
Sulphur SO3 606.8
Chloride CL 217.6
Carbon Dioxide C02 382.9
Hydrogen sulphide H2S 4.5
Total solids 2,396.0
Flow 18,600,000 gallons every 24 hours.
Temperature 135 degrees Fahrenheit.

Reprinted from State Park brochure