Pluto's Cave is a partially collapsed lava tube on the northern outskirts of Mount Shasta, in the Klamath National Forest, about 12 miles northeast of Weed.
It is roughly 190,000 years old, and that is remarkable. Lava tubes do not usually last: their ceilings are only a few metres thick and they collapse quickly in geological terms. This one survives because it sits in a semi-arid climate where erosion is slow, so the roof has had far less working on it than a tube in wetter country would.
Nelson Cash found it in the spring of 1863 while looking for stray cattle. It was explored properly that April and named for Pluto, god of the underworld.
The best account of it is the earliest. William Henry Brewer, assisted by Clarence King, visited on 10 October 1863 on a field trip for the California Division of Mines and Geology, the predecessor of today's California Geological Survey. Writing a month later, he described going to see a cave three-quarters of a mile off, just discovered, of which extraordinary stories were told, and found it quite a curiosity. He set down the country above it too: a gentle lava slope, very rocky, little soil, stunted cedars and bushes, and innumerable lava hummocks a few feet high, with the cave running underneath all of it.
Brewer found the roof broken in near the entrance and multitudes of bats living right to the end of the passage, along with the skulls of mountain sheep that had got in and died. He measured one set of horns at fourteen and a half inches around the base and thirty three inches from tip to tip.
King came back in 1870, by then director of the Geological Exploration of the Fortieth Parallel, and wrote it up in Mountaineering in the Sierra Nevada in 1872. He and a companion tied their mules and went down through a circular hole into an archway of black lava sixty feet wide and eighty high, floored with lava sand and rough boulders, running north under the basalt with barely twenty or thirty feet of roof above them. They followed it half or three quarters of a mile, scrambling over piles of fallen lava that in places brought them nearly to the ceiling, past sides lined with fresh lava-froth and smooth blister-holes, while bats and owls went by on silent wings.
Bring a strong light and a helmet; the far system runs on in total darkness.
Other places on the map within a couple of hours.
