A Southwest Airlines Boeing 737-700, registration N466WN performing flight WN-937 from Oakland,CA to Ontario,CA (USA) with 70 people on board, was enroute at FL390 about 190nm north-northwest of Los Angeles,CA (USA) when the crew initiated an emergency descent to 9000 feet reaching 9000 feet about 9 minutes later (average rate of descent 3333 feet/min) due to the loss of cabin pressure. The aircraft diverted to Los Angeles for a safe landing on runway 24L about 45 minutes after leaving FL390.
A replacement aircraft reached Ontario with a delay of 2 hours.
https://flightaware.com/live/flight/SWA937/history/20120707/1725Z/KOAK/KONT
via Incident: Southwest B737 near Los Angeles on Jul 7th 2012, loss of cabin pressure.