On a recent trip we explored the countryside between Cambria and Paso Robles. This photo is of a walnut grove. When we stopped at a winery I commented about how the bare branches appear to be lavendar-gray. They explained that is because the trees are grafted. The trunks are black walnut, and the branches are English walnut. The black walnut is more disease resistant with other various attributes, but the better nut is the English walnut, so they've found the perfect solution!