What are these little things?

We found lots of these under some deck boards right up against the house. They have the consistency of clay and are about 1/4 inch or slightly smaller. Anyone know what they are?

They are potter wasp nests and it looks like they have all hatched. The potter wasp is a narrow-waisted wasp much like the European paper wasp (EPW) and there are a few Eumenes species in the Pacific Northwest.
Like the EPW, the potter wasp is not overly aggressive. Considered a beneficial insect as they are ferocious hunters of soft-bodied insects like caterpillars and aphids.