The changing leaves of the oaks are another sign of the shift in seasons. Brown is quickly overtaking green, especially in the drier hills. Only the large, lobe-leaved oaks are deciduous–the species with small leathery foliage hang on to their leaves year-round.
California white oak (Quercus lobata) has lobed leaves that are paler beneath and rich, shiny green above. Their acorns are slim, with a large cap-shaped cup that resembles a Rastafarian’s hat. They can be distinguished from their cousins that also have pale underbellies because blue oak has–wait for it–a blueish cast to the upper surface of the leaf. And Oregon oak has a furry coat on its underside (as well as plump, squat acorns). I use the memory-trick that Oregon oaks need such things to grow in the chilly north, whereas Californian oaks have no need for extra insulation.
Identifying oaks can be notoriously tricky, since they cross with one another easily and the results have a mixed blend of characteristics. I tend to stick with the Marin Flora and that keeps me happy. The California white oak pictured here, for example, has shallower lobes than the classic examples. But lobes aren’t an issue in the Marin Flora–so I can happily feel comfortable with my ID.
Note the pale underside of the leaf
Flowers Of Marin 