We have found several of these nests around our property. Many have been in and around our squash area. We have found them in other areas as well. I am guessing, based on observation of our flower visitors that there are probably many other species doing the same thing. I know that many solitary bees and wasps do tunnel nests.
That explains the good pollination I get on my pumpkins. I have a large nesting area in a sandy spot in the driveway and hillside beside it. I have video of them mating over the nest holes. I shared it with Crown Bees but I don't have it uploaded anywhere yet. will try to get that done.