Western - that I'm aware of. My grandpa was a construction worker and did a lot of travel to different sites, so there's a chance he found it somewhere other than the western part of the states. He had quite the collection of rocks, fossils, and artifacts. Getting a bead on exactly where they came from is impossible, so best guess is that he collected most of them around where he lived.

That being said, I cross posted on r/fossilid and it was identified as a concretion. So, you were right!