For years, a pitch black, 20-foot-long crack in the earth concealed a spectacular secret in its depths. Though it’s believed the indigenous Miwok were aware of this subterranean wonder, the caverns didn’t gain public recognition until gold miners swarmed into the area in the 1850s.

Gold-fever inspired a curious prospector to explore the impossible depths of the cave with nothing more than a few candles and a rope. While this explorer was unable to find gold in the cavern, he did find millions of sparkling crystals twisting from the walls in every direction.

These calcite formations, called helictites, are a rare geological treasure. They’re the most delicate cave formations, the natural world’s equivalent of fine China that’s better looked at than touched. Though uncommon, helictites grow in such profusion in Black Chasm Cavern that the cave was declared a National Natural Landmark in 1976.

Helicities aren’t the only wonders waiting within the dark cavern. Its lakes are home to Amphipods, a type of colorless, visionless crustacean. The rare Banksula grubbsi arachnid also dwells within this inky environment.

Adventurous visitors can descend into the cavern to admire its helictites. Modern stairways and lighting allow guided tours of this spectacular cave every day of the year.