Orange Rump Bumblebee
Bombus crotchii is a fairly diverse Bumble bee. Usually it's a duller yellow than the other species. Likes like a dirty old bee. But sometimes it can have orange on it's rump and look pretty.
The natural range for Bombus crotchii is from about Redding south into Baja.
We seldom see them here, but usually once a year one wonders in so the nest must be a 1/2 mile or so away.