Sonoran Desert By Boat

Sea of Cortez

Text and Photos by A.R. Royo

Sea of Cortez

So you want to explore the desert, but you'd rather avoid being stranded alone in some harsh, HOT, life-threatening environment. And maybe you also prefer cool, marine zephyrs instead of hot, dry winds while enjoying the unique plants and animals of the desert environment. And while you're at it, why not throw in a few bird sanctuaries, a whole lot of noisy, barking sea lions, and a tidal differential so great that it makes for some of the best tide pooling on the planet?

Well, if this sounds like your ideal desert vacation, maybe you should consider taking a cruise through the Sonoran Desert. That's just what the Life Sciences Department of Palomar College in San Marcos, California has been doing for more than 20 years. Each spring, the department offers a week-long field trip to the Sea of Cortez to explore the Midriff Islands by ship, skiff, snorkeling and good old bipedal locomotion.

JellyfishSeveral years ago, this DesertUSA correspondent joined a group of biology students and staff, along with some perennial natural history buffs, for a great desert adventure vacation south of the border. My desert cruise also provided a fantastic education (2 units of credit!) and the opportunity to meet interesting new friends.

It included genuine Mexican cuisine morning, noon and night while watching the sun rise and set behind the geologic wonders of a vermilion sea.



The Gulf of California

The Sea of Cortez begins about 50 miles south of where the Colorado River leaves Arizona and dies in the sands near Riito, Mexico. (Before the modern era of dam and aqueduct construction along the Colorado River in the United States, the Colorado River actually emptied into the Gulf of California.) Between these tidal flats and the cliffs of Cabo San Lucas at the southern tip of Baja, 700 miles away, lies the Sea of Cortez, one of the most pristine marine environments left on earth.

Desert meets seaThe Gulf of California is a relatively young sea. Geologists believe it was born during the Miocene, 25 to 30 million years ago, when the Baja Peninsula started to tear away from the mainland of Mexico. Beneath the gulf is a fracture zone that can be traced to California's infamous San Andreas fault. Accompanying this separation from the Mexican mainland was a long period of volcanic activity along the fault, during which time the Midriff Islands, 150 to 200 miles south, were formed.

The nature of the northern Gulf and southern Gulf are quite different, but our field trip was concerned with only the Midriff Islands of the north. The northern Gulf area is unique because of the extremely high tidal displacement, which can be as much as 35-feet at the northern end and remains 5 to 10 feet near the Midriff Islands.

Much of the northern Gulf is fairly shallow, with depths mostly less than 100 feet. The Gulf is shallowest near the Colorado River delta and grows progressively deeper toward the Midriff Islands. However, a 4,800-foot-deep channel lies between the Baja Peninsula and Islas Angel de la Guardia and San Lorenzo. This abnormally deep, yet warm water chasm teems with marine life. Upwelling from below often creates phytoplankton blooms called "red tides," for which the Spanish sometimes called the Sea of Cortez the "Vermilion Sea."

Phytoplankton lie at the bottom of a diverse food chain in this channel which includes a number of marine mammals, including a resident population of finback whales. For this reason, the channel is called Canal de Ballenas (Channel of the Whales). See Desert Cetaceans for more information.

Sea of Cortez and Midriff Islands

The Midriff Islands

When someone mentions the Sonoran Desert, images of a dry, barren, waterless region of southwestern Arizona, with saguaro cactus jutting from the landscape, probably come to mind. So it might be a surprise to learn that the Sonoran Desert reaches across the Colorado River into southeastern California and extends 800 miles south down to the tip of Mexico's Baja Peninsula


Geographers divide the Sonoran Desert into five zones, the driest of which, the Central Gulf Coast Desert, encompasses the Midriff Islands. These islands emerge from the Sea of Cortez (usually called the Gulf of California), which divides Baja California, Mexico from mainland Mexico. Mountain ranges which run the length of Baja create a rain shadow, a barrier for clouds that prevents rainfall from reaching the Sea of Cortez, thus creating these desert conditions.

The Midriff Islands are characterized by small, rugged mountains and hills covered with gravel and loose soil, rock flakes and bedrock. Rain is rare here, but if it occurs at all, it will be late winter or mid summer. Plants tend to grow very low to the ground and have many other adaptations to desert droughts, high temperatures and winds. Animals that live on these islands are able to tolerate very arid conditions and extremely high summer temperatures.

Since most of the islands have no free sources of water, species which depend on free water do not occur on the Midriff Islands. This lack of free water has also discouraged human habitation and has been responsible for the relatively pristine condition of this entire ecosystem.

Because of the isolated nature of some Midriff Islands, there are a number of endemic plant and animal species (especially reptiles) which occur nowhere else in the world. In spite of these harsh desert conditions, there are an extraordinary number of bird species on these islands because marine life, upon which they feed, is so plentiful in the Gulf.

Midriff Island


The Gulf of California's 50- to 100-mile width, an expanse of water that separates mainland Mexico from the Baja Peninsula, is calm and blue most of the time and was, therefore, a welcome refuge for explorers and pirates escaping from the treacherous seas of the Pacific in the 15th century.

After entering this body of water in 1535, Hernando Cortez discovered translucent "black pearls" at present-day La Paz, Baja. He was followed in 1539 by Francisco de Ulloa, who skirted the eastern shore northward to the mouth of the Colorado River, then sailed down the western Baja shore back to the Pacific. It was Ulloa who named this body of water "El Mar de Cortes," but map makers seem to prefer the "Gulf of California."

The priest Eusebio Francisco Kino, after conducting missionary efforts on Baja peninsula in 1683, established a number of missions along the eastern shores of the Gulf in Sonora, Mexico as far north as Arizona. In 1691, he directed construction of the Mission Tumacacori, which remains a National Historical Park just south of Tucson, Arizona.

Because of the harsh desert environment, lack of treasure, Indian hostilities and paucity of water, Baja was virtually ignored for several centuries. Except for the large Isla Tiburon, which contains free water, the Midriff Islands were never hospitable to either Native Americans or the Spanish. While the Seri Indians occupied Tiburon from an early time, this was the only island in the northern Gulf which encountered permanent civilization, from prehistoric or modern peoples.

Heading Out

On the first day of spring, after a chartered bus ride from southern California, our group of 20 arrived in San Felipe, a quaint fishing village located on the eastern coast of Baja California, Mexico. It was midmorning, and the port was full of college students on spring break. They crowded the streets in swim gear or zoomed by in dune buggies and 3-wheelers sporting shorts, sandals and Coronas.

San Felipe's harborWe had only an hour to eat breakfast and tour the shops before piling back on the bus and driving to the harbor a few miles south of the village. Some managed to buy ironwood carvings or last-minute supplies like film, sandals or hats. This was the last time we would see a civilization until we returned to San Felipe a week later.

At the harbor, our chartered, 100-foot ship, the Erik was waiting. We formed a bucket brigade to transfer packs, sleeping bags, gallons of water, snorkeling gear, scientific equipment and supplies from the bus to the ship. We then waited in line as an immigration officer boarded and held court in the galley while we each filed in, showed identification and were questioned. Those who did not have passports were severely rebuked, threatened with expulsion from Mexico, then were finally allowed to continue on.


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