Wind Cave National Park has sandstone, limestone and pegmatite plateaus and ridges. It also has valleys carved into shale and schist.
The region's caves formed as far back as 320 million years ago, when sulfur dissolved the limestone in the area and created the passages.
The cave is famous for what geologists call "boxwork," a collection of thin calcite blades that jut out of the walls and ceilings. These combine to make what looks like a honeycomb of boxes.
Delicate growths of minerals such as aragonite and calcite branch off the ceilings to form "frostwork." This resembles the spreading ice crystals that characterize frost.
Knob-like calcite formations appear on the cave walls. Because of their appearance, they are called "cave popcorn."
The minerals found in the caves include mirabilite, manganese, hematite, Huntite, endelilite, gypsum and Goethite.