The ride that Hard6 and I thought about you on is this one just south of Spearfish.

Take 16 south down to Crazy Horse Memorial (worth seeing). Then backtrack up to 87 (just a couple of miles) and ride 87 (this is the Needles) - GREAT ROAD. You will have to stop at the actual NEEDLE and the tiny tunnel that the road takes through the rock. Continue on 87 - GREAT ROAD - down to where it hits 753. Take a right on 753 down to 16/16-A. Take a left on 16/16-A and then left again when 16-A splits off - another GREAT ROAD. This will take you to Mount Rushmore. Be sure to watch in any tunnel you ride through because the one at the end - MOUNT RUSHMORE is facing you as you turn out of the tunnel.
Trust me brother - you will DIG THE RIDE! Just watch for the forest rat critters.
Anyone going to SD, do the ride - you will dig it.

Making time go by a little faster....sitting over here in Ebolaland thinking about roads I want to see again and roads I missed........See ya'll there! Oh yeah, at the end of the 16-A ride, take a left on 244 (short distance) to go up to Mount Rushmore. We dropped back down 244 and 16-A to Keystone and found a cool place for lunch - that is where we ate the Buffalo Burger. Like I said brother, you will dig the ride!