Wolves have been almost entirely exterminated in the lower 48 states. They are extremely rare. I grew up in Wyoming and way back in the early 1900's, there was a big fat bounty on wolves and they were completely eradicated as a result. Every other state did much the same thing. I think Minnesota might be the only state where the wolf population wasn't hunted to extinction. Yellowstone had wolves reintroduced in the 1990's and is the only place where natural wild herds of bison still roam. It's also got a sizable elk population. If you saw a nature documentary of bison or elk being hunted and killed by wolves then it was probably in Yellowstone National Park. I can't think of anywhere else you'd see all three in the same place. There are no wild mustangs in Yellowstone. There are also no wolves in any area where wild mustangs live that I'm aware of.
There is actually an incredibly small number (~10) of fully wild red wolves still in the Carolinas (I think it's the only wild population left, but I'm not sure), as well as about 100 in North Carolina's "Red Wolf Recovery Area" as part of a reintroduction program. Unfortunately, coyotes have moved in during the wolves' absence, which makes it harder for the wolves to return to the wild, and has led to breeding between the two species when reintroduction is tried. We did exterminate our grey wolf population though, I think the last confirmed sightings were in the 20s or 30s? You do get the occasional hiker or whatever claiming to have seen one still though. We also don't have wild mustangs though, so you won't see red wolves hunting them even if they get their numbers back (though we do have plenty of horses, which do NOT like wolves or coyotes).