Looks like it is more from one of those temperature inversions like at Pittsburg than from any tectonic stuff:

[link to www.nws.noaa.gov]


MID/UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD OVER THE AREA
AS A TROUGH OF LOW PRESSURE OVER THE EASTERN PACIFIC SHIFTS
EAST. UPPER LEVEL MODERATE WEST-SOUTHWEST WINDS WILL BECOME
MODERATE-STRONG NORTHWEST AFTER 29/13Z WHILE MID LEVEL LIGHT
NORTH-NORTHWEST WINDS PREVAIL OVER THE AREA. MIXED WEAK ONSHORE
AND MODERATE NORTHERLY PRESSURE GRADIENT THROUGH 29/02Z AND AFTER
29/19Z OTHERWISE WEAK TO MODERATE NORTHERLY GRADIENT. MARINE
CAPPING INVERSION WAS APPROXIMATELY .4KFT ALONG THE CENTRAL COAST
AND 1KFT OVER KLAX THIS MORNING. THE INVERSION WILL DIFFER BY
PLUS .3KFT OVER THE LA BASIN AND DIFFER LITTLE ALONG THE CENTRAL
COAST MONDAY MORNING. THE CLOUD FIELD WILL CHANGE LITTLE MONDAY MORNING
AND CONTINUE ISOLATED.

MARINE LAYER AT LAX AT 1700Z IS 900 FEET DEEP AND THE INVERSION
TOP IS AT 3432 FEET WITH A TEMP OF 19.2 DEGREES C.