Oh, and a bit more from the museum's website about the crab fossils - they are a temporary exhibit:
They're all from one person who finds round rocks and then removes the surrounding material to show the fossil - and he does this as a hobby! (I find people's hobbies so fascinating!) And some of his fossils are on display at the Smithsonian!
https://ricenorthwestmuseum.org/fossilcrabprep/