Help me identify a bee? - bald-faced hornet

We have a hive in our retaining wall of small black bees with white stripes. They don't seem aggressive but my wife wants to be sure they are ok. They are about a half inch long. I'm going to try to upload a photo.

Ps. I'm in Missoula. If that helps.

I'm not expert but it looks like D. Maculata or the bald faced hornet.

https://www.psu.edu/dept/nkbiology/naturetrail/speciespages/bald_faced_hornet.html
Here is a link to penn states website with some more pictures and information.

I cant see all the markings well in your photo but they do look very similar. The difference I've noted is that yours seem to have made nest in a crack and the typical colony builds a woody material based hanging hive typically.

Good luck finding out what you have! I'd keep my distance and enjoy watching them from afar either way!

Besides the bald-faced hornet, which was already mentioned,  my insect guide shows two black-and- white wasps: potter wasp and mason wasp.  Maybe see if either of those are possible?

those are not bees, they are hornets or wasps. they can sting multiple times, bees can only sting once then they die.

As already stated, definitely a wasp or hornet, not a bee.  The biggest question is - what is your wife's definition of ok?  No matter what they are, if left alone you likely get through the season with few, if any, encounters.  If you start taking that stone wall apart, you likely get stung up pretty good.  I don't know your wife's criteria, how close the wall is to the house, do you have children who play in the area, etc.  

Thanks everyone for your comments. To help further, I was able to capture one as they flew out of the nest.
It's curled up, but you can see the details on the face much better, and the photo with the ruler helps illustrate that it's about 1/2 an inch long (when not curled up).
I took another photo from an angle to get a better shot of the face and tail markings.

As for where the nest is, it's RIGHT next to our outside dinner table. (4 feet from where I sit).
They fly right past my head every minute or so. For that reason, if they are in fact something that could be aggressive, I'm going to have to take action.

Let me know if we're wrong about the Bald Faced Hornet thing.
But it does seem to have 2 sections.. more wasp like than bee.

It looks like a bald-faced hornet to me. We have quite a lot of them this year also. I have not noticed them to be aggressive or bothersome, they mostly just go after nectar.  However, I have never stumbled across a nest. In my guidebook it says "They will readily sting to defend themselves or their nest" Also says there will be a large paper nest.

Thanks to all. Sadly, due to the location near our outdoor dining area, I decided on extermination. If they were farther away I would have left them alone. Have a good day everyone.