One of our favorite activities in the Black Hills of South Dakota is to take a slow drive along the scenic Iron Mountain Highway where many of the one-way tunnels form a picture frame around Mount Rushmore. I also love the unique engineering design in the pigtail bridges used in place of hair pin turns to navigate down the side of Iron Mountain.

We are camped near Custer State Park and the town of Custer in the southern part of the Black Hills at Custer's Gulch RV-Park. It is an OK commercial campground just like dozens of others in this area.

Pigtail Bridge on the Iron Mountain Highway in the Black Hills of South Dakota

In order for some of those tunnel shots (of Mount Rushmore) to work many of the tunnels emerge into essentially "thin air". Road builders designed a series of pigtail bridges as a solution. Pigtail bridges perform the same function as switchbacks. They move traffic from one elevation to another as easily as possible. Since these tunnels popped out into thin air these bridges were constructed from the mouth of the tunnel and in a sweeping motion corkscrew down. This picture was taken immediately after exiting one of those tunnels. You can see how the road corkscrews around and passes under the bridge. A pretty impressive piece of engineering that I have only seen here in the Black Hills.

Another pigtail bridge on the Iron Mountain Highway in the Black Hills of South Dakota

This is another of those pigtail bridges on the Iron Mountain Scenic Drive. In one place I think they string two of them together as the highway really drops in elevation.

Pigtail bridge on the Iron Mountain Highway in the Black Hills of South Dakota

This is another view as we pass under one of those pigtail bridges.

Remember that pigtail bridges cross over the road they are constructed on in an effort to change elevation rapidly. Look closely at this arrangement and you can see we are rapidly losing elevation via that pigtail bridge arrangement.

Pigtail Bridge on the Iron Mountain Highway in the Black Hills of South Dakota

Yet another pig tail bridge. I can not tell from this picture but I suspect a tunnel is on the right side of that bridge.

Pigtail Bridge in Wind Cave National Park south of the Black Hills in western South Dakota

By now pigtail bridges are becoming as common as flies around a feed lot. Not really but there are a number of these engineering marvels located throughout the Black Hills. I think this one is located in Wind Cave National Park south of Custer and north of Hot Springs.

That is all there is.