Holy crap.... is this B. insularis? Uploading six photos.

Not B. vosnesenskii despite the cloudy yellow face, as I believe the yellow setae on anterior thorax rule this out. Yellow setae on face rule out B. californicus. Doesn't look like any of the B. occidentalis morphs I've seen, and it doesn't match any of the several morphs of B. flavidus I have seen here (nor does it appear "shaggy" enough), nor B. fervidus (though I suspect fervidus remains a possibility).

This was a HUGE bee, perhaps the largest bumble I've observed in the garden.

I saw one of these before once, at about 5,000 feet above sea level...
(https://www.inaturalist.org/observations/85878680)

...but my house is only at 1,000 feet above sea level.

I'm in the Cascade foothills, so geographically this observation seems plausible. But the elevation seems pretty uncommon.