I purchased a tree that was displaced by development some years ago. With the help of a local tree surgeon/sawyer, I milled the tree into slabs, air-dried them in my backyard for 2-3 years, and have built a number of these coffee tables.
The slabs are California Claro Walnut, which has been used for centuries as the root stock in local walnut orchards. In all of these slabs, you can clearly see the line at the top where the Claro Walnut was grafted to the fruit-bearing English Walnut. I have seldom seen more beautiful wood with greater variety of color. There are blues, blacks, and purples in the midst of the swirling red, brown, and orange.
The bases are made of Piedmont Poplar -salvaged from a tree in Oakland.