Thanks for the comments, guys.
Beetleman, sedums are very common at higher elevations in my area. The way they grow here, they fully deserve their name. Stone crops, that's where you'll find them. The one shown here is unusually succulent, with those bladder-like leaves.
I just looked up
Sedum in Hitchcock & Cronquist, "Flora of the Pacific Northwest". It seems there are only two species in this area that have opposite leaves on the flower stems. Only one of those is listed in the University of Washington's
online herbarium. So if I had to bet, I'd put my money on
Sedum divergens. But I can't really distinguish it from
Sedum debile, which is not shown in the online herbarium and which Hitchcock & Cronquist distinguish by technical characteristics that can't be seen clearly in this photo. So since I don't have to bet, I think I'll just leave it as "some kind of
Sedum".
--Rik