It’s common knowledge that water is the bane of fire, but the Earth tells us a different tale.
Up to about 200 million years ago, at the dawn of the Jurassic Period, there was no California. It might be said that even North America didn’t exist. North America had then part of the supercontinent of Pangaea, which was about to break apart.
As ancient peoples once imagined their world an island in a great sea, so Pangaea was an island in a great sea. For eons, the rivers of Pangaea carried sediments to that sea, loading down the dense, cool crust beneath the waters. That crust, it turn, was floating upon an ocean of lithospheric mantle, but the crust was getting heavier and losing its buoyancy, until finally it gave way, and began to list like a ship giving in to the sea.
Around Pangaea, ocean floors began to dive beneath it for the same reason, leading to what we know today as the Pacific Ring of Fire, and the Triassic supercontinent began to fracture under the strain of the spreading triggered by the suction of ocean floor subducting into its perimeter.
Here on the eastern shore of the great ocean, the Farallon Plate was born out of the disintegration of Pangaea. As this young oceanic plate dove under Pangaea (and later Laurasia), the uppermost layer of the plate was scraped off and piled against the edge of the continent, and so Cascadia was born. Cascadia is that land commonly known today as the Pacific Northwest. When California was young, it was part of Cascadia.
The continent was pulled westward and stretched along its margin, giving rise to the forearc basins known today as the Puget Sound, the Willamette Valley of Oregon, and California’s Central Valley.
The water-loaded serpentine hydrated the rock beneath the continent, liquefying the rock and causing streams of melt to form. This led to the formation of a volcanic arc along the Pacific Coast, and deep below, the plutons that would eventually uplift to become the Sierra Nevada and Klamath Mountains of the present.
The hydrated magma streams that feed the volcanoes of Cascadia are not pacified by their water continent, but contrarily, rendered all the more volatile by the resulting steam, making for explosive releases of subterranean fire, not unlike the sudden expansion of a grease fire when fed with water.
Down in Cascadian California, there was no San Andreas Fault, nor any great granitic Sierra Nevada. These and other characteristic features of present-day California would arise as the trailing edge of the Farallon Plate began to disappear under North America.
To be continued …