A series of column transport experiments ranging from 25ºC to 275ºC, as well as batch sorption experiments at 25ºC, were conducted to estimate cation exchange parameters for lithium and cesium at the Newberry Crater Enhanced Geothermal System demonstration site.. The experiments were designed to facilitate interpretation of single-well field tracer tests to interrogate fracture surface area. Lithium column transport from 125ºC to 275ºC showed a strong temperature dependence, with much greater cation exchange at higher temperatures than in 25ºC experiments. Cesium column transport at 225ºC indicated a weaker temperature dependence, and unlike Li + , its exchange decreased at higher temperatures.