Moaning Cavern is a solutional cave located near Vallecito, California in the heart of the state's Gold Country. It is developed in marble of the Calaveras Formation. It was discovered in modern times by gold miners in 1851, but it has long been known as an interesting geological feature by prehistoric peoples. It gets its name from the moaning sound made by water dripping into small holes at the bottom of the "chocolate waterfall" flowstone formation, causing a drumming sound, which would echo off the cave walls and be carried by the wind out of the natural entrance of the cavern. The portion of the cave developed for tourists consists of a spacious vertical shaft 165 feet tall, which is descended by a combination of stairs and a unique 100-foot-high (30 m) spiral staircase built in the early 1900s. It is open to the public for walking tours, rappelling, and spelunking. Including the off-trail areas, the cave reaches a depth of 410 feet.
Moaning Cavern is also an archaeological site, where some of the oldest human remains known in America were discovered. The cave has long been the resting spot for the bodies of prehistoric people who fell into its opening. The bones were preserved by the mineral-rich water in the cave.