Lava River Cave, near Bend in central Oregon within Newberry National Volcanic Monument, is Oregon’s longest known continuous lava tube, with a northwest passage of 5,211 feet. Formed about 80,000 years ago by a lava flow from near Mokst Butte, it became hollow when molten rock drained from beneath a hardened surface. Native Americans knew the cave before Euro-American settlement, though settler Leander Dillman is credited with its first recorded discovery in 1889. Its present name dates to a 1923 geology study by Ira A. Williams. The cave’s collapsed entrance, ice chamber, Echo Hall, Sand Garden, and specialized cold-adapted life make it a notable and accessible volcanic site.