Derrick Cave

Derrick Cave is out on its own, in the remote northwest corner of Lake County, Oregon, on BLM ground. It runs about 1,200 feet, and it is big: up to 80 feet wide and 46 feet high in places, which puts it among the roomiest lava tubes in the state.

It is also the reason the country around it exists in the shape it does. Lava flowed south from a large vent north of the cave, and the same eruption built Devils Garden, a 45 square mile lava bed southwest of here. Most of the rock in Devils Garden was delivered through this tube. It began as an open channel, roofed itself over as the surface crusted, then drained when the vent shut off, leaving the tunnel. Sections of that roof later collapsed, and those collapses are now the entrances at the north and south ends.

The age is bracketed rather than fixed. The flow is no older than about 13,000 years, and no younger than 6,845 years, because Mount Mazama tephra from the eruption that formed Crater Lake blankets the whole Devils Garden surface, including the ground above the cave.

The strangest chapter is Cold War era, and it starts earlier than you would think. During the Second World War local residents planned to use Derrick Cave as an air raid shelter if Japan began bombing the west coast. That was never needed, but in 1963 the cave was formally designated a nuclear fallout shelter, with food and water for up to 1,200 people stored in a side passage behind a locked steel door. Vandals broke the vault open repeatedly and by 1970 the food was all gone. They left the civil defense water cans, most likely because the water had frozen solid. Camping is not allowed in or around the cave.

Getting there means gravel roads and no services, so carry fuel, water and a spare tyre, and do not rely on a phone signal. Most of the time a two-wheel-drive, high-clearance vehicle reaches the trailhead, but four-wheel drive may be needed when the road is wet, and in the rainy season and winter it can become impassable for anything. The cave is open to the public year round, unlit, with a rough and blocky floor in places. Bring two lights each and something on your head.