Two Rock was once a landmark on the trail between Petaluma and other Coast Miwok communities near Bodega Bay. Avoiding low, wet areas, the path skirted the valley and passed between two large rocks sitting on top of a small hill.

When Fort Ross was built, a Mexican military outpost was established below Dos Piedras (“Two Rocks” in Spanish) to discourage further Russian expansion. This didn’t stop Russian princess Helena de Gagarin, wife of the fort’s commander, from passing through Two Rock in the 1840s.

In that same era, Dos Piedras was used to mark the spot where four ranchos met.

During the Mexican War, John C. Fremont and Kit Carson passed through Dos Piedras. A few years later, “Two Rocks” post office was established. Eventually, the “s” crumbled away, leaving “Two Rock” behind.

Geologically, the rocks date to the heyday of the dinosaurs, around 100 million years ago. Formed by tectonic forces beneath the ocean as the Pacific plate was pressed under the North American plate, they’re part of what’s called the Franciscan Formation. After the dinosaurs were gone, uplift and erosion eventually exposed them to the surface.

During World War II, Two Rock again became a military outpost. Its primary mission was intercepting Japanese radio communications with antennas that remained in operation during the Cold War. Once again, soldiers at Two Rock were keeping an eye on the Russians. Most of the base was transferred to the Coast Guard in 1971.

Dos Piedras is no longer much of a landmark. Traveling by car, it’s easy to miss a pair of big rocks on a hill. Those rocks sat still while we humans sped up and moved on. And they’ll still be sitting there when these days are long forgotten.

Arthur Dawson is a Glen Ellen-based historical ecologist. Reach him at baseline@vom.com.