At 5,466 feet in length (just over a mile), Lava River Cave is Oregon's longest intact lava tube and an absolutely unique adventure for anyone visiting central Oregon. In contrast to Lava Butte, which was formed roughly 7,000 years ago, Lava River Cave is estimated to have been formed around 80,000 years ago from an eruption that flowed as far north as Redmond, Oregon.
Lava tubes form as the top layer of a lava flow is exposed to air. The air cools the lava, and it slows as it begins to solidify. Meanwhile, the lava lower down remains at temperatures as high as 2,000 degrees Fahrenheit and continues to flow like a river below the hardened top crust. If the river has the opportunity to drain, the lava tube remains. The mile long segment of the tube that flows downhill toward the Deschutes River is not the only portion of this large formation. The entrance of the cave actually lies on top of a collapsed area of the tube, and in the other direction the same cave extends an additional 1,560 feet uphill. This portion of the cave is unfortunately not accessible to the public due to unstable rock.
Interestingly, the lava tube was first recorded in 1889 by Leander Dillman. However, the presence of crafted obsidian flakes hints at earlier use by native Americans. It was presumably used for storing meat in the summer and perhaps even for winter shelter.
Be sure to dress warmly for the cave, as the temperature quickly drops to an average of 42 degrees. It's a good idea to bring flashlights or headlamps, and for a modest donation you can also rent one of the Monument's propane lanterns.