That would be Crandall Creek. Yep, MT (and WY) have some serious undercuts so best to be on your game there.
However, the play can be as fun as anywhere I've been. Check these out, all within an hour of Bozeman:
Yellowstone River, Gardiner Run: Park and Play at the take out:
American Whitewater - playtime in yankee jim
Yellowstone River just west of Big Timber, "float and play":
American Whitewater - NWRI - Yellowstone 2. Boulder R. to Clarks Fork Yellowstone R.
Further downstream of this wave, at lower flows is one of the best waves to learn on, called Mrs. Bubbles.
On the east side of Big Timber, just a few miles down the freeway, still on the Yellowstone, there is another "float and play" run that includes two great features:
Four Banger: Great wave play on 4 waves in one rapid (short stroll back to the top)
Greycliff: A super mellow wave with eddy service that is just right for perfecting your spins, etc.
Last, but not least, Mr. Bubbles is on another "float and play" on the Stillwater.
American Whitewater - NWRI - Stillwater 3. Cliff Swallow public access to Whitebird public access
Missoula is a really fun area too. There is a fun feature right in town: Brennan's Wave. There are also some fun runs close by, including some reasonably "easy" creeking.
I like both towns a lot but prefer Bozeman personally. The calling card for Missoula however is the much milder weather, so the play boating season lasts longer. Both towns have lots of outdoor types in residence, along with universities, making for fun nightlife. Either way, you should be a happy camper!