North of Sacramento to Chico. The #2 of these examples is most applicable. Tip- If depictions of walnuts are used, they should represent the mature product. This is what most are used to seeing. The whole walnut in it's tan shell or the cross section of that same image exposing the meat of the nut inside. Also, Leaves should be more "leaf shaped". English Walnut (very different from Black Walnut) leaves have a distinct traditional leaf shape. A "flowing" or "whisky" leaf representation may be appropriate, if used.
OK I will research the English Walnut look... I think it is hard to make a walnut look like a walnut and be simple... would love to find a way to avoid using gradients so you have more flexibility with the logo.