Q: I don’t know what animal(s) built these “shelters”, but am curious if you can provide any guidance. Do you have any ideas what built these?

A: You are the host of dirt dauber wasps. They are considered beneficial because they stuff their mud tubes with spiders, including black widows. After provisioning the tube, they lay their eggs on the bodies of their prey. If their messy mud tubes outweigh their benefits you could control them with a surface spray of cypermethrin (Demon) or deltamethrin or permethrin every couple of weeks.

dirt dauber nest

dirt dauber nest