A series of one-way high frequency acoustic propagation experiments were conducted off southern California in an area east of San Clemente Island. Source and receiver were located at depths of 137 and 107 m, respectively, below the diurnal thermocline. The source frequency was 30 kHz; the pulse duration was 0.5 ms and the pulse repetition rate was 0.5 s−1. A series of fixed ranges were used extending from 180 to 920 m. In addition, temperature fluctuations were observed over the experiment depth range with a thermistor array. For a representative data set, energy density spectra of the acoustic and temperature fluctuations reveal similar forms. At a range of 385 m with a record length of 1 h (1800 transmissions), the standard deviation of the received acoustic intensity was 0.5 dB with a coefficient of variation of 12%. The sound-speed fluctuation patch size was calculated to be 1 m. [Work supported by NAVSEA.]