Well, I am no expert but looks like the Mastodon tooth I owned. A lot like it. And the Mastodons are believed to have disappeared around 10,500 years ago, toward the end of the Paleo Period, I think. If I remember correctly.
Nice find... I hunted the Missouri river gravel beds as well as the creeks and streams when I lived in Columbia, Mo. I found a lot more nice artifacts hunting water than I did hunting the fields.