I could be wrong, but I believe that the only difference between California English, English, Turkish, or Circassian is where it is grown. It is all the same species, Juglans Regia.
That said, I bought four very nice blanks on Ebay several years ago when I made a typo and incorrectly searched for "Frech" walnut blanks. Since the seller listed them incorrectly as Frech Walnut, apparently no one else was looking. They actually did appear very much like what we consider to be French Walnut, having a lighter color and much less mineral streaking than most California grown English, and much lighter than Turkish or Circassian. They also had very small pores and great grain layout and figure and the seller sent me four extra forearm blanks. So apparently some of the genetic characteristics will express themselves even when the nuts are grown far from France in entirely different soils.
