Oregon Caves National Monument

Oregon Caves National Monument and Preserve in Josephine County, about 20 miles east of Cave Junction in the Siskiyou Mountains of southwestern Oregon, protects a rare marble cave system formed by the dissolution of limestone and marble by mildly acidic groundwater over millions of years. The cave is the only marble cave on the Pacific Coast open to the public for guided tours, distinguishing it from more common limestone formations found in other US cave systems. Guided tours — the only way to access the cave interior — depart daily from May through October and traverse approximately half a mile through a series of passages, rooms, and chambers decorated with stalactites, stalagmites, flowstone, cave bacon (translucent banded mineral sheets), and aragonite nodule formations. The cave maintains a consistent temperature of 44°F (7°C) year-round, making a light jacket or fleece essential regardless of outdoor conditions. The 90-minute standard tour covers the main passages and is the only option for most visitors; a longer Off-Trail Adventure tour for ages 10 and older explores less-visited sections by headlamp. Above the cave, the monument's 4,070 acres include old-growth mixed-conifer forest and river headwaters. A trail network of approximately 10 miles begins at the cave entrance; the Big Tree Loop (3.3 miles) passes a Douglas fir estimated to be 1,200 years old and among Oregon's largest trees. The Oregon Caves Chateau, a six-story rustic lodge built in 1934 inside the cave entrance valley, is a National Historic Landmark open for lodging and dining during the summer season.