The heat discharged by the hot spring system in Long Valley, California, has been estimated from measured spring discharges by using geochemical mixing models. Of the total flow of 1300 1/s from 11 thermal springs in the caldera, approximately 20% or 250 1/s os contributed by the hydrothermal system at depth with temperatures near 210¿C. The effects of heat loss by conductive cooling, mixing, and boiling are qunatified for the springs in Hot Creek Gorge, which are the major source of hot water discharge in the caldera. The estimated total convective heat discharge is 4.3¿107 cal/s, which is in agreement with an estimate obtained from the rate of boron discharge from the caldera into Lake Crowley. To supply heat conductivity to circulating water of meteoric origin at a rate of 4.3¿107 cal/s requires a heat flux at depth in excess of 10 μcal/cm2/s.