Hadenoecus subterraneus (Scudder, 1861) - cave cricket inside the entrance to Great Onyx Cave.

Great Onyx Cave is located in the northern part of Flint Ridge in Mammoth Cave National Park, Kentucky, USA. It has 8 miles worth of mapped passages. Geologically, Great Onyx Cave is part of the Mammoth Cave System, but it has become erosively separated from it (although an air flow connection with the Mammoth Cave System has been identified). Great Onyx Cave is the downstream continuation of the Salt Cave section of the system.

The walls of Great Onyx Cave are limestones of the Paoli Member, shales of the Bethel Member, and limestones of the Beaver Bend Member of the Girkin Formation (lower Upper Mississippian). The travertine speleothem-rich areas of Great Onyx Cave are wet and occur where a cap of overlying Big Clifty Sandstone is absent. The dry portions of the cave are below an intact Big Clifty Sandstone "caprock", and include the giant canyon passage areas and the gypsum speleothem areas.

The main cave passage of Great Onyx Cave is called Edwards Avenue. It is a giant canyon passage at Level B in the Mammoth Cave System. Level B passages formed about 2 to 4 million years ago during the Pliocene.

This cave is sometimes accessible to the general public by guided lantern tours during boreal summer months. This photo was taken during a field trip in June 2011 as part of a cave geology course at Mammoth Cave park.