Unfortunately, she would not show me her butt.
27Apr_Bombus_vosnesenskii-3. Head hair is short and even. Yellow abdomen hair band does not extend ventrally with a few yellow hairs. Bombus caliginosus is a possibility in Eugene, and the ones I have collected have dark amber tibial spurs. (Vos has black) But you wouldn't see that in most photos.
27Apr_Bombus_mixtus on Plectritis congesta
Certain of year and month, guessed on day.