Low‐frequency (<50 Hz) sound transmission studies were conducted off Mission Beach, California. Sound from both explosive and cw sources, as received on bottomed geophones and hydrophones cable connected to the NOSC Oceanographic Tower, were used to determine the transmission paths and propagation loss. Sound speed and other parameters of the sub‐bottom layers, as determined by divers, bore holes, and refraction shooting, were used as input to a FFP computer program to model the propagation loss. The computed propagation loss is less than that observed at short ranges (<2.5 Km) and greater than observed at longer ranges. The discrepancy is believed due to a slope reversal of the interface between the unconsolidated and the semiconsolidated layers. Propagation was best in the E–W direction, but the noise level was also higher. The buried hydrophones were quieter than the bottomed hydrophones and the S/N ratio of the E–W and vertical geophones was greater than on the hydrophones at 5 and 15 Hz. At these very low frequencies and short range the S/N ratio of the geophone recordings was greater than that on the hydrophone recordings.