[mortonarb.org] Range, Habitat, Height: Quercus dumosa is known to occur within Orange, Santa Barbara, and San Diego counties in southern California, and extends slightly into Baja California, Mexico. It is very habitat-specific and is found in chaparral communities on coastal bluffs, hillsides, canyons, and mesas, where it usually dominates or codominates. This evergreen shrub thrives in very sandy soil, establishing an extensive root network, and typically reaching between one and three meters in height. However, heights to five meters have been observed in canyon bottoms of San Diego County (A. Meyer pers. comm., 2018). (link added by Mary Ann Machi)

[Wikipedia] Allergenicity: The species is a severe allergen, with pollination generally occurring in spring. (link added by Mary Ann Machi)