Best Walnut Species without Irrigation

Does anyone here have any experience with Walnuts in this climate? I've heard English walnuts are often hit by early frost?

English/Persian Walnut
Butternut
Heartnut
Buartnut
Black Walnut

Any cultivars you can recommend would be great as well.

 I'm farther South than you (S. Willamette Valley),  but we have half a dozen Walnuts trees on our place.
A few were planted by my grandpa when he was a kid ( he doesn't know the specific variety, but says they are English Walnuts grafted on Black Walnut rootstock). Those are still producing some at 85 years old or so. They get no supplemental irrigation.
 We have a fifty-year-old Butternut tree (gets some Summer watering). We hardly ever eat them because they are hard to crack out.  But the kids do eat some. Also the hulls make Khaki dye, and I've heard you can pickle the underripe fruit.
 I have planted a few new Walnuts that are around eight years old (Idaho Carpathian, Cook's Giant, Rodhouse).  They produce modest crops of tasty nuts.  But I irrigate them a few times throughout Summer.  Last year I OVER-irrigated and broke off a big limb from the Cook's Giant.  I also have two seedling Heartnuts (still tiny, but scrappy).
 I notice a lot of wild Black Walnuts in the area that get no special attention.  Also seedling English-type Walnuts that squirrels plant seem to do fine on their own.    I recently colllected a bunch of Black Walnuts and seeded some droughty, sandy ground that will get no irrigation... we'll see how they do.  
 Good Luck with the Nuts!
 

I think all walnuts are pretty drought tolerant once established. But I think that English (Persian) and California black walnut would be better in dry conditions as they both evolved in arid regions (English walnut mostly hails from central Asia/the middle east, even the Carpathian may originally hail from there). They're only called English in the US because they were introduced from the UK

James Landreth wrote:I think all walnuts are pretty drought tolerant once established. But I think that English (Persian) and California black walnut would be better in dry conditions as they both evolved in arid regions (English walnut mostly hails from central Asia/the middle east, even the Carpathian may originally hail from there). They're only called English in the US because they were introduced from the UK

Depends, wild stock english walnuts are beastly strong and usually provide a decent harvest even in a dry year. Most black walnuts available in the USA are wild stock and most english walnuts available are from not wild stock. For wild stock I'd definitely say hands down the Carpathian walnut wins for a west coast sort of environment. But if the soil is fairly deep and fine grained I'd lean towards a wild black walnut having a slight win over a domestic English walnut in terms of dry year fruit set, but not by much. Blacks are more tolerant of long hot moist weather compared to the English, hence why they have done so extremely well on the east of the Mississippi.

Sure beats hickory who decides dry years mean its time to produce almost nothing. I love the taste of hickory nuts but I wish I could depend on them in tough times more.