Southern California black walnut (Juglans californica) is a deciduous tree or shrub-like tree with multiple trunks. It has large, divided leaves and thick bark that is deeply furrowed when the tree is mature. This tree is now endangered in large parts of the southern portion of its natural range, due to development. 

The nuts are edible but hard to remove from the shell so these trees are not planted for agricultural use.  However, birds eat the nuts and like to nest in the branches.  

This hardy tree tolerates heat, smog, and drought and is great on slopes.  It does best in moist areas and can handle garden watering.  Toxins in walnut seeds will typically prevent other plants from growing under the tree, so don't try to put understory plants too close.