South Dakota officials are inspecting seven scenic tunnels in the Black Hills this week for structural integrity. Engineers and a geologist are monitoring the tunnels on Needles Highway and Iron Mountain Road to determine unsound rock, weathering and erosion. They do so by gently tapping hammers onto the tunnels, which were blown out of granite with dynamite in the 1920s. The inspection comes as the Federal Highway Administration requires more routine checkups every two years. South Dakota officials aren’t concerned the tunnels will collapse, but the tunnels will gradually erode, just like any rock shelf.