Quercus oblongifolia | Los Angeles County
These are leaves of Mexican Blue Oak (Quercus oblongifia) from the California State University at Fullerton Arboretum in the Los Angeles area. These leaves differ in shape from what is considered the idealized Mexican Blue Oak leaf form, but definitely display the expected coloration. The difference in shape could derive from the fact that the tree is an ecotype from an area in which the Arizona White Oak (Q. arizonica) occurs, as the leaf shape includes hints of that species, and the two do co-occur in many places. There is also a chance that the tree is a hybrid with acorn derived from a Mexican Blue Oak grown in cultivation, such as at an arboretum, and has been fertilized by an unknown oak. Given the intensity of the coloration, it is more likely the former case than the latter.