Buffalo Before Breakfast (Magic Tree House Series #18)
BUFFALO BEFORE BREAKFAST
Osborne, Mary Pope

Jack and Annie are ready for their next fantasy adventure in the bestselling middle-grade series—the Magic Tree House! 

Hello, buffalo!

That's what Jack and Annie say when the Magic Tree House whisks them and Teddy, the enchanted dog, back almost 200 years to the Great Plains. There they meet a Lakota boy who shows them how to hunt buffalo. But something goes wrong! Now they need to stop a thousand buffalo from stampeding!