rodent builds using wattle and daub

I'm not sure if this is remarkable or normal. We've got some land in Southern Utah, and there's a big pile or rocks where rodents (wood rats? field mice?) build their nests. Around the property they generally stack dead sagebrush branches into a pile for their nests. There's one nest in the rock pile, however, where clay has been incorporated into the nest. This is the second year I've seen it. The first, only a small amount of clay was placed on top of the wood, but his year it's quite a bit.

I'm curious how common this practice is. Have others seen it? On the left in the second photo, you can see a "normal" nest without daub. On the right is the daubed nest.