Glenwood Springs, Colorado, and surrounding areas. Volcanic activity below heats up underground water forcing it up through fissures in the mountain to the spring at the surface. The spring flows at an amazing 3.5 million gallons per day making it one of the largest in the world. Mineral-rich water is captured at 122 degrees F allowing the therapy pool to be kept at a soothing 104 degrees F and the main pool at 90-93 degrees F. The pool is open year around.