English: Limestone karst in the Mississippian of South Dakota, USA.

South Dakota's Black Hills have many limestone cave systems, including two of the world's longest caves - Jewel Cave and Wind Cave. Seen here is the natural entrance to Wind Cave - it leads to an extensive and complex maze of passages, of which about 154 miles are currently mapped. Both Jewel Cave and Wind Cave are developed in paleokarst zones in the Lower Mississippian Pahasapa Limestone. These caves don't extend up to outcrop areas for the most part - they end updip and they end downdip. Cave development started during the Pennsylvanian, long before uplift of the Black Hills Dome and the Laramide Orogeny. Pennsylvanian sediments fill some of the paleokarst at Wind Cave. Sometimes, the Pennsylvanian fill has been secondarily removed, resulting in a paleocave.

The modern structure of the Black Hills (= Phanerozoic sedimentary rocks dipping away from a large Precambrian basement core) has played a role in enlarging the Late Paleozoic paleokarst, via mixing of waters. Caves are known to enlarge in mixing zones, where groundwater masses that have different chemistries meet. Mixing has been concentrated at the old paleokarst zones.

Wind Cave is named for the strong breeze encountered at this small opening.

Locality: natural entrance to Wind Cave, southern Black Hills, southwestern South Dakota, USA (~43° 33' 29.56" North latitude, 103° 28' 46.26" West longitude)