Pluto's Cave is a partially collapsed lava tube on the northern outskirts of Mount Shasta in the Klamath National Forest. Its main entrance is located close to the 99-97 Cutoff c. 12 miles (19 km) North-east of Weed and c. 14 miles (23 km) East-southeast of Grenada. The tube is roughly 190,000 years old, which is quite old for a lava tube, as they normally collapse quickly, having ceilings only a few metres thick. However, Pluto's Cave is located in a semi-arid climate, where erosion is restricted, which contributes to its survival.