"A sharp tooth shape appears in a rocky mouth of Caverns of Sonora, Sutton County, Texas, USA. The world-class Caverns of Sonora have a stunning and sparkling array of speleothems (helictites, stalactites, stalagmites, flowstone, coral trees, and other calcite crystal formations). National Speleological Society co-founder, Bill Stephenson said, after seeing it for the first time, ""The beauty of Caverns of Sonora cannot be exaggerated...not even by a Texan!"" Geologically, the cave formed between 1.5 to 5 million years ago within 100-million-year-old (Cretaceous) Segovia limestone, of the Edward limestone group. A fault allowed gases to rise up to mix with aquifer water, making acid which dissolved the limestone, leaving the cave. Between 1 and 3 million years ago, the water drained from the cave, after which speleothems begain forming. It is one of the most active caves in the world, with over 95% of its formations still growing. Sonora Caves are on Interstate 10, about half-way between Big Bend National Park and San Antonio, Texas."