Onyx Cave

Onyx Cave is a series of passageways and rooms that honeycomb an outcropping of limestone in the Santa Rita Mountains. Limestone formed from the remains of tiny sea creatures deposited in layers over a vast period of time. Eventually, geological forces deformed and cracked the limestone. Water entered these cracks and gradually enlarged them into what is now known as Onyx Cave.

The cave is first mentioned in the accounts of pioneer ranchers and miners who came to the area in the 1870s and 1880s, although we know that Onyx was used by a succession of hunters, explorers and Indians because of various artifacts found in the small shelter cave adjacent to the main cave. The remains of a mill foundation can still be seen at the bottom of Onyx Hill. In the 1940s and 1950s, the cave became a favorite spot for adventurous people to explore. Increased use led to heavy vandalism. Broken formations and paint-scarred walls became the rule, not the exception. In 1963, the entrance was gated in an effort to preserve the remaining beauty of the cave. The gate was dynamited after a very short time, and no further efforts were made to save the cave until Escabrosa Grotto, Inc., leased Onyx and gated the entrance in 1974. Since that time, several large-scale cleanup and repair projects and numerous one day efforts have restored much of the cave’s former beauty.