Neffs Cave, Limestone cave in Mount Olympus, United States.
Neffs Cave is a limestone cave on the slopes of Mount Olympus in Salt Lake County, Utah. The cave follows a single vertical fissure that drops deep into the mountain, making it one of the deepest cave systems in the state.
The cave came to wider attention in 1949 when John and Jamie Lyon were trapped inside for three days. After their rescue, the National Speleological Society began formal mapping work in 1957 to document the full extent of the system.
The cave takes its name from the Neff family, who once lived at the base of Mount Olympus. Today, local caving clubs manage access and share knowledge about the geology of the Wasatch Range.
Access to the cave is only possible for experienced caving teams with proper gear and official authorization. Anyone interested in visiting should reach out to local caving groups in advance, as they coordinate access and safety oversight.
The cave sits directly on the Wasatch Fault, an active geological fault line that runs beneath the Salt Lake Valley. An underground river flows below the vertical fissure and can be seen by caving teams who reach the lower sections of the system.
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