The geologic setting of the Presidio has much to do with its special natural history. Titanic earth movements occurred here 100 million years ago, when one enormous tectonic plate slipped like a huge serpent beneath another plate. This movement is called “subduction.” One result of this slow-motion collision is a soil called … not surprisingly … serpentine. Serpentine soil hosts a special plant community called serpentine scrub ... one of many native plant communities at the Presidio. Fast forward 99-million years, and sand dunes began forming. The dunes are the result of yet another massive geologic event … the end of the last Glacial Period. As the planet warmed, the glaciers melted, the seas rose and the dunes were born. All this happened in the blink of a geologic eye … less than 10,000 years ago. The dunes host yet more unusual plants.
Situated on the northern tip of the San Francisco peninsula, the cool Pacific waters surrounding the Presidio produce a moderate Mediterranean climate. This climate, coupled with a unique blend of serpentine soils and mobile sand dunes, sparked an explosion of plant and animal life adapted to the unusual conditions here.
PLANTS AND ANIMALS
The plants created worlds within worlds as each species carved out an exclusive community of life. The Presidio holds an unusually high number of rare and endangered plants. For example, the roots for the endangered Presidio Clarkia (Clarkia franciscana) can traced to the unusual serpentine grasslands found here. Beautiful wildflowers abound in the spring and summer, and the Presidio's animals include over 200 species of birds.
One odd twist of fate: The U-S Army is the reason the Presidio is like an environmental lifeboat. The Army focused construction in only certain areas. The rest of the undeveloped land was left … undeveloped. Because it was a military base, civilian access was also limited. The native plants and animals were protected as a by-product of military priorities.