Hi Shaktari, 

Great picture! These are introduced European wool carter bees (Anthidium manicatum). The males will often patrol patches of plants in the mint family, aggressively excluding other bees from the patch as a way to attract females to the patch to mate with (pictured here). Watch closely and you may also see the females scrape the trichomes (i.e., hairs on the plant) into a small "wool" ball, which she will use to protect her brood from parasites. These bees nest above ground like mason bees, and are, in fact, in the same bee family as mason bees and leafcutting bees. 

Andony

Thanks for the wonderful explanation.  I'm wondering if you can be a bit more precise.  Are both bees from the same species, one male and one female, or is one bee trying to get rid of the other?  

Of course. Same species - male on the top and the (smaller) female on the bottom. We also have a number of native Anthidium species, particularly in Southern Oregon, which share the brightly colored integument of this introduced species. Keep your eyes out - you should have incredible bee diversity out there. There are over 700 species in Oregon and we have an effort to document their occurrence and ranges in Oregon, the Master Mellitologist program (which contributes specimen-based records to the Oregon Bee Atlas):
https://extension.oregonstate.edu/bee-atlas

I greatly appreciate the clarity, thank you!