There was an almond planting along the highway north of Yakima but I think most of it got pulled out awhile back. But surely there have been others in the area also. And the spontaneous seedlings you have seen might originate in some other way, like from home plantings or maybe even spilled open bags of nuts.

On this side of the mountains I have seen squirrels going for hybrid almond tree nuts in the middle of a block with few other trees nearby for them to scramble up to safety on. And the street they were scampering across was quite wide, yet they were so interested in the bounty that they risked running around out in the open.

there are references to almond production in WA.

Almonds in Yakima - who knew? thanks Bboy.

No squirrels in this area I'd be willing to bet, at least no tree squirrels. Hardly any trees, and these particular trees are always when I see them isolated on dry hillsides surrounded by sagebrush and cheatgrass. Would magpies cache nuts in the ground like jays and squirrels do? or ground squirrels maybe.

Come to think of it there are plenty of naturalized walnuts in the area though all in narrow riparian zones where they get water, unlike these trees, but probably spread the same way, something relatively big caching large nuts. I'd presumed the walnuts originated with old homesteads as they grow where I'd want to put a house, while the almonds are far from good home sites.