ABSTRACTTemperature logs were used to study the movement of water injected into wells penetrating the Pliocene Ogallala Formation in the High Plains of Texas. Descriptions of the results of three recharge tests are necessary because the hydrologic response to recharge at each site was very different. The water used for artificial recharge of the aquifer was derived from playa lakes in which the diurnal fluctuation of temperature was as much as 17 ° Celsius. Daily thermal cycles that resulted from injection of this water were traced through the aquifer by use of a series of temperature logs made at frequent intervals in cased holes specially constructed for logging. The thermal pulses were detected by logging holes as far as 46 meters (150 ft) from the recharge well.In areas where this technique was used, the Ogallala Formation consists of thick sections of uniform medium‐grained sand that visually appear uniform and thus were thought to have uniform hydraulic conductivity. However, the results of temperature logging at each of the three sites clearly demonstrate that the hydraulic conductivity varies greatly through these seemingly uniform lithologic units. Thermal pulse velocities as high as 4.6 meters (15 ft) per hour were found in thin zones immediately adjacent to sand where velocities were a few feet per day. Tracing with temperature logs is potentially useful in locating zones of high intrinsic permeability and in detecting apparent changes in rate of flow as a function of ti