Now hold up a second, friend, and put your hand flat against one of these roadcuts. Feel that? Cold stone, quiet as anything. But this rock is a traveler, and it has come a mighty long way to sit here under your palm.
The whole headland you're standing on — geologists call it the Franciscan Complex — is ocean floor. Not shore rock. Deep-ocean floor, hauled up into the daylight. Look close at the roadcut and you'll see three kinds of storyteller. There's pillow basalt, lava that erupted straight into cold seawater and froze into humps like a heap of sacks. There's graywacke, old muddy sand pressed hard as iron. And there's the beauty of the bunch — that ribbony red chert, layer on layer of it, hardened from the ooze of tiny sea creatures called radiolarians, drifting down and settling on the deep floor grain by grain, patient beyond telling.
Here's the wonder of it. That red chert, and the pillow basalt with it, were born somewhere out in the equatorial Pacific, way south of here, far from any shore. Then a great slab of ocean crust went diving down beneath the edge of the continent, and as it dove, some of that far-traveled floor got scraped off — like mud peeling off a boot — and plastered right onto the edge of the land. Carried north the long slow way, over roughly a hundred million years. The graywacke's more of a homebody — muddy sand shed off this very continent's margin and dumped into the trench where all that scraping happened. We're talking the age of the dinosaurs, give or take — Jurassic into Cretaceous, and I'll keep the numbers loose, because deep time doesn't keep a tidy ledger.
So there you are. You climbed a hill to look at a bridge, and you ended up leaning on rock that crossed an ocean and rose from the black deep to meet you. Take a breath of that fog and just let it sink in a minute.
