What did Louis and Clark discover?

This week on Science Fiction Theater!

Louis and Clark set out on their mission expecting to find predatory mastadons in the West. What if they did?

Well, the easiest answer would be they weren’t predatory mastadons (what a stupid idea), but s North American Pleistocene megafauna like sabretoothed cats and  ground sloths. Just say the natives didn’t wipe them out. But then, what DID the natives do with them?