These cork trees are from the Napa Valley area of California.
Cork trees are a renewable resource in that they live anywhere from 150 to 250 years. Their bark or cork can be harvested every 10 to 12 years. Over 50% of the world's cork for the wine industry comes from Portugal, with the rest from Spain, Italy, France and some from Africa.
From a distance the bark looks like bark, but up close it looks almost spongy. Interesting tree.