It is difficult to lump together all the areas of California in a kind of weather summary as the area covers quite a variety of slightly different climates due to the spread of the state and the fact that California has both coastal and mountainous areas, with weather patterns differing between these areas.
However, overall California is said to have a Mediterranean type climate with warm summers and mild winters. Temperatures however, will hit more extremes on the hot and cold fronts in the mountainous areas where winters can get much colder and snowy and summers are warm and dry.
With San Francisco being further north than, say, Los Angeles, it has a warm climate but is susceptible to fog, particularly in the summer, whereas Los Angeles, being further south, has weather that can be very pleasant in the summer with temperatures in the low 80’s in the summer and not getting too cold in winter with temperatures in the 60’s.
So if you are looking for California weather averages then you really need to be specific as to what area you are checking as you could be surprised if you just take an average weather temperature for the whole county.