Oregon Caves National Monument and Preserve, Marble cave system in Josephine County, Oregon, United States

Oregon Caves National Monument and Preserve is a marble cave system in the Siskiyou Mountains featuring stalactites and stalagmites carved by water erosion over thousands of years. The site also protects surrounding forest and wilderness lands that frame the underground passages and create a complete natural environment.

Local explorers discovered the caves in the late 1800s, bringing the site to regional attention. President William Howard Taft established it as a national monument in 1909 to preserve the cave system for future generations.

The name River Styx, given to the cave's underground stream, comes from Greek mythology's river linking Earth to the Underworld. In 2014 Congress added this stream to the National Wild and Scenic Rivers System, the only subterranean river in that system. No evidence shows the Takelma or other native peoples used the cave.

The cave interior remains a constant 44 degrees Fahrenheit (7 degrees Celsius) year-round, so bring warm layers for any visit. Guided tours are required to safely explore the marble passages, which include stairs and narrow sections.

In 1877 Elijah Davidson and his brother Carter, with four others, explored the cave and found four distinct levels, opening passages blocked by stalactites and stalagmites and locating what is now called Exit 110. The stream inside the cave is named the River Styx after Greek mythology; in 2014 it was added to the National Wild and Scenic Rivers System as its only subterranean river.