Southwest Airways Flight 7 originated at San Francisco, for Los Angeles, with stops scheduled at San Jose, Watsonville, Monterey, Paso Robles, San Lois Obispo, Santa Maria, Santa Barbara, and Oxnard. Departure from San Francisco was 18:00, 15 minutes behind schedule. Flight 7 proceeded in a routine manner and landed at Santa Maria at 20:10. All previous scheduled stops had been made with the exception of the one at San Luis Obispo which was passed over because of local weather. Departure from Santa Maria was at 20:18, 12 minutes behind schedule. Two minutes after takeoff from Santa Maria the flight radioed its on and off times to and from that station and gave an estimated arrival time of 20:39 at Santa Barbara. This was the last radio contact with the flight. The crew should have used the 4000 feet minimum altitude to remain VFR above the clouds, but instead where at 2740 feet MSL in instrument conditions. The aircraft struck the gradually rising slope of a ridge. PROBABLE CAUSE: “The failure of the flight, for undetermined reasons, to maintain the specified minimum en route altitude of 4000ft for the route being flown.”