Meanwhile, on Reddit: https://www.reddit.com/r/fossils/comments/1c4hldl/found_a_mandible_in_the_travertin_floor_at_my/
Note the abundant comments on Reddit, many by "experts", all saying definitely hominid, most probably human, and - depending where quarried, from 200 - 300, 000 years to possibly millions of years old. And somewhere, somebody's walking over another cross-section of said person...