I noticed this Hymenopteran while I was photographing a nearby shrub. I believe it's a female, perhaps a masarid wasp...though that may be wrong, as the antennae do not seem clubbed. (However, it was not at all aggressive, which makes me think it's not a yellow-jacket.)

After it caught my attention, I watched it enter a small nest hole in the cliff-side about chest-high. It then flew up the cliff-side a small distance and promptly returned. After it repeatedly did this, I realized this was a fine opportunity, so I found a good position to support my camera (on the rock surrounding the nest site) and focused on the nest hole. Sure enough, the wasp continued to sally back and forth. And though it was fairly speedy, I was able to get some good shots by being "set-up" already.

As this series of images shows, she was collecting small pebbles up-slope and using them to plug-up the entrance to her nest upon returning. By the time I took the last shot, she had finished and the nest entrance hole was no longer obviously visible (see last image in series).