The Ultimate Guide to Adventure in Oregon

"The Lava River Cave, located 12 miles (19 kilometer) south of Bend on the east side of Highway 97 and part of the Newberry National Volcanic Monument, is a prime example of a lava tube. Measuring in at 5,211 feet (1,588 m) in length, the northwestern section of the cave is the longest continuous lava tube in the state of Oregon. Although the official discovery of the cave was credited to a pioneer hunter back in 1889, archaeologists have found the presence of obsidian flakes near the cave and believe that Native Americans knew about the cave long before settlers ever arrived in central Oregon. 80,000 years ago a volcanic eruption formed the Lava River Cave. The volcanic flow that formed the cave also underlies much of the Bend area, and even almost reaches Redmond, Oregon. The Lava River Cave itself was created by lava flowing from a volcanic vent that flowed northwest from the vent toward the Deschutes River." - ATLAS_OBSCURA