View photos of the edible and medicinal plant, Juglans californica (California walnut), profiled in Wild Edible Plants of California.

A passage from Wild Edible Plants of California:

California walnut’s original distribution (especially NorCal walnut) is limited and considered rare. Through a century–plus of cultivation and plantings, both species are now relatively abundant, though it is thought that most current specimens contain some DNA from Black (Juglans nigra) or English walnut (J. regia).