Annie's Canyon Trail in Encinitas's Cardiff-by-the-Sea district is a quarter-mile slot-canyon loop inside the 979-acre San Elijo Lagoon Ecological Reserve. Restored and reopened on June 21, 2016, by the Nature Collective conservancy, the trail channels hikers through naturally eroded sandstone walls that narrow to shoulder width before climbing to a 200-foot overlook with panoramic views of the Pacific Ocean and San Elijo Lagoon, terrain that complements the wave-side instruction offered by Buenas Olas Surf School at the coast below. Two route options split at the canyon junction: a strenuous one-way passage requiring ladder-stair climbing and hand-over-foot scrambling, or a moderate switchback ascent rising 300 feet in a quarter mile. The reserve's seven-mile trail network connects Annie's Canyon to the La Orilla, Rios, Santa Inez, and Pole trails through salt-marsh, riparian-woodland, and coastal-sage-scrub habitats that shelter over 100 documented bird species. Hikers finishing the canyon loop can extend south along the coastline to Cardiff State Beach where the lagoon channel meets the Pacific at the base of Restaurant Row. The slot canyon's Torrey Sandstone formation dates to the Eocene epoch and features mushroom-cave erosion patterns, Liesegang banding in iron-oxide-stained strata, and cross-bedded sedimentary layering visible at eye level throughout the passage.