The Natural Bridge Caverns are the largest known commercial caverns in the U.S. state of Texas. The name is derived from the 60 ft natural limestone slab bridge that spans the amphitheater setting of the cavern’s entrance. The span was left suspended when a sinkhole collapsed below it.
The caverns are located near the city of San Antonio, Texas in the Texas Hill Country next to the Natural Bridge Wildlife Ranch, a drive-through wildlife safari park. The caverns feature several unique speleothems and other geological formations. The temperature inside the cave is 21 degrees Celsius (70°F) year-round and the humidity rate is a constant 99 percent. The deepest part of the public tour is 180 feet below the surface, although undeveloped areas of the cavern reach depths of 230 feet.
The caverns are still slowly developing. Due to the porosity of the limestone, rainwater travels downwards through the layers of rock, where it dissolves out calcite, a weak mineral that makes up all of the speleothems at Natural Bridge Caverns. After exiting the limestone, water enters the caverns where it flows and drips constantly throughout, causing the formations to retain a waxy luster that can be seen in a few caverns.
This article uses material from the Wikipedia article “Natural Bridge Caverns“, which is released under the Creative Commons Attribution-Share-Alike License 3.0.