La Jolla Cove's seven sea caves were carved over two million years by Pacific swells eroding the Ardath Shale Formation, creating a half-mile chain of sandstone chambers accessible only by water. The largest, Sunny Jim Cave, extends 145 feet inland and was named in 1902 by author L. Frank Baum for its profile resembling a British cereal mascot. The cove itself became California's first underwater ecological reserve in 1971, protecting 533 acres of kelp forest and rocky reef habitat where water temperatures hover between 59 and 68 degrees year-round. Seven distinct caves punctuate the coastline between Shell Beach and Boomer Beach: Clam's Cave, Seal Rock Cave, White Lady, Little Sister, Arch Cave, and the twin formations known as the Emerald and Sunny Jim. Each chamber displays stratified sediment layers from the Eocene epoch, visible as horizontal banding in hues of ochre, rust, and charcoal. The caves flood at high tide and drain to exposed floors at extreme low tides, though safe access requires midpoint tidal windows when swells remain below four feet. Geologists note the formations recede an estimated six inches per decade due to ongoing wave erosion. The marine reserve status prohibits fishing and collecting, allowing populations of California spiny lobster, giant sea bass, and Garibaldi damselfish to recover to densities rarely seen elsewhere on the Southern California coast. The kelp canopy shelters juvenile white seabass and halibut through summer months. California sea lions haul out on the rock shelves flanking the caves between December and May, while harbor seals occupy the beaches year-round. La Jolla Cove and Cave snorkel tour routes typically navigate the outer cave mouths during calm morning conditions, when visibility exceeds 20 feet and planktonic interference remains minimal. The sandstone composition creates refracted light effects inside the caverns — emerald and sapphire tones visible only during midday sun angles between April and September. Wave-cut benches inside the caves display fossilized mollusk impressions from the Paleogene period. The 1100 Coast Boulevard access point, managed by San Diego Lifeguard Services, offers stair entry to the rocky beach platform where guided La Jolla Cove and Cave snorkel tour groups launch kayaks and distribute snorkel gear. Winter storm surges occasionally deposit cobalt-blue sea glass fragments eroded from pre-1970s dumpsites, now prized by beachcombers despite collection prohibitions within reserve boundaries.