Thermal (15--30 ¿C) springs issuing from 1912 ash-flow tuff in the mid-valley region of the Valley of Ten Thousand Smokes consist of meteoric water that may have been heated by an incompletely cooled lens of welded tuff upvalley from the springs. Conductive cooling of the thermal waters along the flow path is the likely cause for the difference between the observed spring temperatures and the source temperature inferred from chemical geothermometry. Conductive cooling alone can not easily account for the seasonal fluctuations in spring temperature, however. Mixing of the thermal waters with cold meteoric waters would seem a likely possibility; but thermal water chemistry is constant, indicating that mixing does not occur after the water leaves the zone of heating. Even if mixing occurred, simple mixing models do not account totally for the observed temperature differences of the springs from late spring to summer. The geochemical and thermal data argue for a complex hydrological and thermal regime.