They are formed from water that is heated underground and returned to the surface. In certain areas, magma or lava has worked its way up through the Earth's crust to relatively shallow depths below the surface. Ground water percolates downward, comes in contact with the hot rock and is heated. As the water returns to the surface, it collects into pools known as hot springs. Temperatures and water flow vary by area and may change over time due to earthquakes or other natural phenomena.
Many hot springs have long histories of special status with Native American tribes.
They used hot springs for healing and believed the waters had other powers. Native Americans had a tradition of declaring a hot spring to be a neutral zone, devoted to peace and healing. In the 19th century it was legal and often quite profitable to claim that mineral water had the ability to cure an impressive list of ailments. Numerous hotels and boarding houses sprung up near the springs, catering to visitors looking for relaxation and cures. There are over 1,700 hot springs in the western United States.