>>>not sure what to expect<<<
Us either :)
But recently it has been pleasant during the day (mid 60s to 70) and cool to downright freezing in the wee hours of the night and early morning.
Layering is the usually the key to Southern California in the Winter & Spring.
As an FYI, I wear shorts every day, all year, when I don't have to be in a business suit.
Check out a weather forecast
It is rarely 80deg in March at the coast! IF you want that sort of heat you can drive inland 2hrs to the desert. Layers is always the answer here. Don't just bring one sort of clothing . Bring a little of everything.