Valley oak is the largest of the western deciduous oaks and is common through California's interior valleys and foothills. Occurring in loam soil and slope habitats.

Valley oak, or it's subspecies, is also known locally as:  white oak, bottom oak, swamp oak, and water oak.  The two to four inches long leaves are matte green above and pale green below.

Gall formation begins when a wasp deposits its eggs into plant tissue, causing minor local swelling around the eggs. Once the larvae emerge from the eggs, their chemical secretions stimulate a response from the host plant, and the site gradually develops into a tumor-like growth.  These galls can be caused by the gall wasp (Cynipidea) or California gall fly (Andricus californicus).   (While galls are common on all oaks, the blue oak has the greatest variety of galls.  It is not uncommon for a single specimen of blue oak to have galls from 20 to 30 species of wasps.)

Identification of oaks, due to hybrids and variability within the species, is a challenge. Related species of oaks from the same subgenus may share similar characteristics and oaks belonging to a single species may be quite different due to environmental influences. The oaks adapt to the changing climatic conditions, and this adaptation may change the leaves and acorns in both size and shape.