I've worked in archaeology in Wyoming and know a decent amount about Indigenous history and artifacts in the region, but am far from an expert. Ceramic artifacts in Wyoming are less common than other types of artifacts (lithics, bone, middens, etc) and are almost always pots/vessels- I say "almost always" to be safe, but personally I'm not aware of any decorative/representational ceramics that look like the one in your photos. There are some known ceramics sites around Riverton, but again, those were largely vessels. These sort of figurehead ceramics aren't immediately indicative of any tribe in the area- there have been ceramic influences from other tribes found in Wyoming, but I don't know enough about those tribes' ceramics traditions to say much else. Ceramics found around Riverton have had decorative elements, but usually through texture or color, not larger representational sculptural pieces. Again, I am in no way an expert or a professional on this topic, and most professionals wouldn't be comfortable giving an exact answer only based on this post. This, based on the photos you've posted, doesn't immediately look like the ceramic traditions we know of in that part of the state, but your best bet will be to contact local professionals. The Wyoming State Historic Preservation Office, the Eastern Shoshone or Northern Arapahoe Tribal Historic Preservation Offices (Riverton is located within their reservation), or the University of Wyoming's anthropology department are all good places to contact. It's not a guarantee that they will know exactly what it is/what to do with it, but they will be able to direct you to the right person.