Pluto's Cave is a partially collapsed lava tube on the northern outskirts of Mount Shasta. The lava tube is roughly 190,000 years old which is pretty old for a lava tube since they normally collapse rather soon with their ceilings being only a few meters thick. However Pluto's Cave is located in a semi-arid climate where erosion is restricted which would account for its long age. In 1863, Nelson Cash discovered the lava tube and named it Pluto's Cave after the Roman God of the underworld. However, lots of evidence was found that showed its use by indigenous people long before Europeans arrived. Visitors can safely hike into the cave about 1200 feet (350 m) of the cave.[1]