Blue oak woodland is found in the inner coast ranges and the Sierra Nevada foothills, surrounding the Central Valley. Primary species are blue oak and interior live oak (or on west facing slopes facing the exterior ranges, particularly in Contra Costa and Alameda counties, coast live oak takes interior live oak's place), together with valley oak, canyon live oak, California scrub oak (Q. berberidifolia), gray pine, California buckeye (Aesculus californica), and western redbud (Cercis occidentalis).
Coast live oak woodland is widespread in northern and southern California, and is dominated by coast live oak, together with California buckeye, Pacific madrone, California bay, and California walnut (Juglans californica).
Valley oak woodland is found in the interior valleys of northern, central and southern California, and is dominated by valley oak and coast live oak, together with gray pine and Coulter pine (Pinus coulteri).
Status and future of California oak woodlands
Blue oak woodlands cover about 2,939,000 acres (11,890 km2) of the state, and of this area about 79%, or 2,322,000 acres (9,400 km2), shows no evidence of past cutting of trees. Recent research by the University of Arkansas Tree-Ring Laboratory has studied several unlogged stands of blue oak woodlands, and suggests that the state may harbor over 500,000 acres (2,000 km2) of such old growth forests. This would make California's oak woodlands some of the most extensive old growth forests left in the state. However, most oaks of full tree size are more than one hundred years old, and few saplings are ever produced, because cattle often tear the plants to pieces.
The Oaks 2040 survey estimates that 750,000 acres (3,000 km2) of California oak woodlands are seriously threatened by 2040 as a burgeoning state population makes ever more use of the wildland. This comprehensive survey includes oak woodland maps and inventory data for the ten oak types found in California. By evaluating this new information against current State of California economic growth projections, the location and extent of oak woodlands most at risk of development are identified.