Sea Lion Caves are a connected system of sea caves and caverns open to the Pacific Ocean at Sea Lion Point, about 36 miles (58 km) south of Newport and 11 miles (18 km) north of Florence, Oregon. The cave system extends for 1315 feet (401 m) and is the longest in the United States and the 10th longest in the world. The main cavern has a floor area of about 2 acres (0.81 ha) and a vaulted rock dome about 125 feet (38 m) high. Southward from the main chamber, a low passage runs 1,000 feet (300 m) to a sea-level opening. This corridor is flooded at high tide and free of water at low tide. The western entrance is a short, high passage through which the ocean washes at all tide levels. At the north end of the system, a third entrance is about 50 feet (15 m) above the ocean which serves as an elevated observation area where the entire cave system and its wildlife are visible to the public. Visitors descend 208 feet (63 m) by elevator from a commercial gift shop on U.S. Highway 101 to the observation platform. It is the only mainland rookery of Steller sea lions in the contiguous United States and is home to about 200 cows, yearlings, and immature bulls.
The caves were discovered in 1880 by Captain William Cox, who first entered through the western channel in a small boat on a calm day. He purchased the land in 1887 from the State of Oregon and his family owned the property until 1926 when R.E. Clanton purchased the property from the Cox estate with business partners J.G. Houghton and J.E. Jacobson. There were no roads in the area at that time and the slopes above the headlands were used for sheep pasture. In 1929, the partners dropped a rope ladder to a primitive footbridge leading to the north entrance of the cave. In 1930, it became clear that the Oregon Coast Highway would be built between Florence and Newport, and the partners gained permission to build a parking area east of the new highway and a gift shop on the west side. They carved a trail by hand along the cliff face to access a wooden tower that enclosed a staircase bolted to the cliff face at the cave’s north entrance. Sea Lion Caves opened formally to the public in 1932. The highway was a gravel road until 1934, however, word of the attraction spread and the number of people visiting the Sea Lion Caves slowly grew until 1942, when virtually all recreational travel halted during World War II. Meanwhile, Clanton withdrew from the partnership in 1934, and R.A. Saubert became part owner. In 1958, work began on an elevator that descends to an observation platform above the cavern. It took three years to build and cost $180,000 to construct due to salt and moisture issues. The three families continued to operate the Sea Lion Caves until 2006 when the Houghton family withdrew and the Saubert and Jacobson families took over the partnership.
The promontory at Sea Lion Point developed where basalt flows accumulated to great thickness. Flows of dense, hard basalt and interbedded fragmental rocks are characteristic of promontories on the Oregon coast. A narrow ledge is present in many places near the base of Sea Lion Point and represents a platform that developed by wave erosion on less resistant fragmental basalt. A significant factor in the erosion of sea caves in basalt promontories is the extent to which the rock has been broken along fracture zones. Fracture zones are places of weakness and erosion proceeds at a greater rate there than where the rock is intact. Broken rock along the fracture zone is quarried by the forces of water under hydraulic pressure and compressed air and over time is enlarged. The caves at Sea Lion Point were localized by intersecting fracture zones, one trending roughly north-south and the other in a nearly east-west direction. The largest opening is along the east-west fracture and is the one used by the animals as they move in and out of the cave. A tunnel that passes through the headland was developed along the north-south fracture zone and the fractures are visible in the ceiling of the tunnel. Lateral erosion within the cave and dislodging of rock from the ceiling have shaped it into a large, high-vaulted, amphitheater-like cavern with the height of a 12-story building and stretching the length of a football field. It is the natural home to a colony of sea lions and a diverse array of seabirds and shore creatures. See a video of the caves here. Read more here and here. Explore more of the Sea Lion Caves here: