Subway Cave, located in Lassen National Forest, California, was formed 30,000 years ago by a lava flow in the Hat Creek Valley. During the flow, the top cooled and formed a hard crust while allowing hot lava to continue to flow underneath. Eventually, the lava stopped flowing, leaving behind this shell. Subway Cave is about a third of a mile (half a kilometer) in length.
Add to Cart Add to Lightbox Download