unknown mud insect nesting
What an interesting find. Those look like nests of a species of mud dauber wasps, there are more than one species in Oregon. They are solitary wasps that do not defend the nest and rarely sting. The super good news is their prey is spiders. If you do not mind the nests where they are, then leave them to hatch and eat spiders. University of Maryland Extension and Iowa State University Extension both have publications with more information regarding these fascinating insects.