Out in the middle of the Gulf of California, in the channel that narrows between Baja California and the Sonoran coast, there is a scattering of rock islands that nobody lives on. San Lorenzo and San Pedro Mártir are two of them, protected as part of the Islands and Protected Areas of the Gulf of California. The Midriff Islands are famous among naturalists because the tides here move enormous volumes of water through narrow gaps, which churns up nutrients and feeds one of the richest marine systems on Earth. Whales, dolphins, sea lions, and clouds of seabirds all come for the harvest.
San Pedro Mártir is the dramatic one, a steep volcanic cone whitened by guano, thick with blue-footed and brown boobies, pelicans and cormorants, with giant cardon cacti on its slopes. San Lorenzo is a longer, lower ridge of rock, desert in its heart, and home to a sea-lion colony and specially adapted lizards and rodents. You cannot ride to either of them, of course. The point on the map is a spot in open water, and visits are by licensed boat from the peninsula, with strict rules on landing and distance from wildlife.
So the riding part belongs to the shore. The usual departure is Bahía de los Ángeles, on the Baja side, reached by Highway 12 from the transpeninsular road, a good paved ride of about an hour through boojum trees, cardón forests, rocky hills and then a sudden drop to a blue bay with islands lying offshore. The road is straight in places, with a few gentle bends and dips, and wind can be a nuisance, especially in winter and spring when northerlies come down the gulf. Heat in midsummer is intense, so the cooler months, from October to April, are the sensible time. Whale sharks gather in the bay in warmer months, and fin whales are seen in spring.
Services are modest. Bahía de los Ángeles is a small fishing and sport village with a couple of stations or fuel sellers whose supply can run short, so take fuel at the main highway junction and carry extra. There are family restaurants serving fresh fish tacos and shrimp, small hotels, and campsites on the beach. Bring water, sun protection and cash in pesos, since cards are patchy, and book any boat trip ahead through a licensed operator.