Rush Warm Spring
Rush Warm Spring emerges at just 72 degrees Fahrenheit near Bellevue in Blaine County, making it one of the cooler thermal features in the region. The water is warm enough to distinguish from groundwater but too cool for traditional hot spring soaking except on the hottest summer days.
The spring sits at 4,770 feet elevation in the high desert landscape east of Bellevue, where sagebrush dominates and annual precipitation barely reaches 14 inches. Snowfall averages 45 inches, light by Idaho mountain standards. A walk of roughly 2,330 feet from Austin Road crosses open, arid terrain to reach the source. The water feels tepid rather than warm, a subtle thermal anomaly in an otherwise dry and wind-swept landscape.
The modest 28-degree differential between water and air temperature suggests a shallower circulation path than Idaho's hotter springs, or significant mixing with cool groundwater before surfacing. The spring sits on the eastern edge of the Snake River Plain volcanic province, where residual heat from past volcanic activity still warms groundwater across a wide area. Note that the Wikipedia entry attached to this spring actually describes Carson Hot Springs in Nevada, a data error.
This is not a soaking destination in the traditional sense. Water at 72 degrees feels cool to most bathers except during summer heat. Access requires a walk of about a third of a mile from Austin Road. The area is open and exposed with no shade or facilities. Bellevue and Ketchum are the nearest towns for supplies. Visit in July or August if you want the warmest combined experience.