Hello,
A colleague of mine shared some pictures of an interesting rock she found. It was found loose by a creek in the Denver area. It looks to me very much like an inner era, although it may well be something else. None of us are able to positively identify it. I'm sure someone here can confirm whether or not it is a fossil, and what it might be. The creek in question flows from the east, and my understanding is it would have to be a tertiary or quaternary fossil if it is indeed a fossil.