This study focuses on the evaluation of solar thermal energy storage in a medium-scale soil-borehole thermal energy storage (SBTES) system installed in San Diego, CA. The SBTES system consists of an array of thirteen 15 m-deep, closely-spaced borehole heat exchangers installed in conglomerate bedrock. The entire site is above the water table, with relatively dry subsurface conditions. Instrumentation was included into the array to monitor temperature distributions with depth and radial spacing within the array, as well as water content fluctuations near the ground surface. A total of eight evacuated tube solar thermal panels with an absorber area of 4.16 m2 were connected in series to supply heat to a temporary heat storage tank. Results from a 4-month transient heat injection period into the SBTES system are presented in this paper. These include data on the characterization of the thermal properties of the SBTES system, the transient heat flux collected from the solar thermal panels, the corresponding transient heat flux into the subsurface, and the changes in ground temperature.