Natural Bridge, a two-hundred-foot-tall limestone arch estimated to weigh thirty-six thousand tons, formed through the slow dissolving of limestone by carbonic acid created when water and carbon dioxide mix. In limestone terrain, this process can create caves, underground rivers, and sinkholes as the rock is worn away. Around one million years ago, Cedar Creek was swallowed by a sinkhole and became an underground river that eventually reached the James River through a cave developing in the limestone deposit. Over several hundred thousand years, these small forces carved out the surrounding walls, and when the Cedar Creek-made cave collapsed, Natural Bridge remained standing at the narrowest point in the chasm. Taller than the Statue of Liberty without her base and Niagara Falls, Natural Bridge is the tallest limestone arch in North America and rises to nearly nineteen stories.