Coronado Islands

Islas Los Coronados are a chain of four granitic fault-block islands strung about 8 kilometers northwest to southeast in Mexican water, roughly 15 miles south of San Diego and about 7 miles south of the border. From north to south the group runs Coronado Norte, the small pyramid of Middle Rock, Coronado Centro, and Coronado Sur, the largest of the four at about 2 miles long and rising to 205 meters at its southern summit. The rock is granite and metamorphic basement, part of the Peninsular Ranges Batholith, not the volcanic material sometimes assumed offshore. Steep escarpments drop straight from the cliffs into a rocky bottom, giant kelp fringes the shores, and within a short distance to the west the sea floor plunges past 1,100 meters. A charter out of San Diego reaches the islands in about an hour.

The water at the islands runs clearer than anywhere on the mainland San Diego coast. Typical days give 30 to 70 feet of visibility, the average sits near 50 feet, and the clearest days do better still. Two things drive that. The islands stand on the edge of the continental shelf, so deep cold currents sweep them with clean pelagic water from offshore. They also sit well south of the Tijuana River outfall and of the runoff, harbor discharge, and coastal plankton bloom that thicken mainland water through much of the year. Each island's east side stays sheltered from the prevailing northwest swell, so the lee dive sites remain calm on days when the mainland is choppy. Counterintuitively, visibility often improves as the swell picks up, because the added offshore mixing works in the islands' favor.

Human traces on the islands are limited but distinctive. On the cliffs of Coronado Sur, above Smugglers Cove, the stone foundations of a Prohibition-era casino and hotel still stand, opened in 1933 to serve American drinkers, abandoned after Mexican gambling restrictions, and reduced to footings by a 1988 storm. A California sea lion rookery occupies North Coronado, a small northern elephant seal colony lives on Middle Island, and the island group holds one of the largest known nesting colonies of Scripps's murrelet.

The exposed granite ledges and boulder slopes at sites such as Lobster Shack, Keyhole, and Middle Grounds make this a rocky reef biome. Along the fringing shores, giant kelp anchors on those same ledges in the shallows and grows up through the water column to the surface, adding a kelp forest biome layered over the rock. Deep water starts almost immediately beyond the cliffs, with the shelf edge inside a few hundred yards, so a pelagic biome overlays the site as well, and blue-water species pass through in season.

Access is by charter boat only. Operators run out of the Point Loma sport-fishing landings, H&M Landing, Fisherman's Landing, and Point Loma Sportfishing, and out of Mission Bay's Seaforth Sportfishing, with dedicated scuba and freedive outfits such as Waterhorse Charters and Just Get Wet making the same crossing. The open-water leg of about 15 nautical miles is the main variable, trips cancel in bad weather or heavy winter swell, and currents at the exposed sites run strong.

The islands lie in Mexican federal waters within Baja California and fall inside a Mexican wildlife refuge managed by CONANP. Going ashore is prohibited, and only the Navy detachment and the lighthouse keeper live on the group. Spearfishing on scuba is prohibited nationwide in Mexico, so spearfishing at the islands is freedive only; scuba diving for non-spearfishing purposes is allowed. Every visitor needs a valid US passport, a Mexican tourist permit, a Mexican fishing license, and a CONANP conservation pass, all arranged through the charter.