Custer State Park is literally awash with wildlife. From bison, big horn sheep, burros, mule deer, antelope and a variety of other animals it is a wildlife lovers delight.
However even driving at 25-35 mph we nearly ran into two deer who ran right across Wildlife Loop Road in the middle of the day. Fortunately we did not hit any of the animals. However from what we understand this is a frequent occurrence. Particularly when scanning the hillsides for other animals someone just happens to run right in front of you.
Unfortunately on the southern end of Needles Highway right before Wind Caves National Park we ran over a rather large squirrel who was trying to cross the road under our wheels. So please be on the look out for critters large and small in this scenic area.
If you are going to drive on the "Needles" highway (us87) or the "iron mountain road". Any vehicle larger than a standard pickup truck may be in danger! There are low narrow rock tunnels(that a large vehicle can not go through) and very tight turns (switch backs) that low or long vehicles can at get stuck on. The roads are also very narrow, so the possibility of turning around just is not there for any thing larger than a car. These roads also have incredibly steep grades that can and do take drivers by surprise. Brake fade is common. These are very beautiful places, but leave the motor home in the campground! Enjoy, but take precaution!
As you go through the hills, there are several tunnels you must pass through. Be sure to take your time (and your turn) so that accidents are avoided. Only one car can make it through at a time.