Terrane Terroir and What’s Up with this Purple Dirt Anyway?

As far as we can tell dinosaurs did not drink wine. Yet while the dinosaurs were leaving their bones in the mud farther east in Utah, the dirt that would become Hidden Ridge was being washed into the sea on to a narrow continental shelf and cascading in underwater landslides into the trench where the ocean floor was sliding under an island arc something like the island arcs in Southeast Asia today.

These offshore sediments gradually accumulated over a period of about a hundred million years into a linear terrane that underlies most of the coast ranges of California. This terrane is suitably called the Franciscan after the good Fathers on donkeys that first brought vineyards and winemaking to the state.
Terrane, terroir, but not terra firma. Certain chemical processes when sediments are compressed and melted into rock form magnetic crystals that align with the North Pole when they form. From these we can tell that Hidden Ridge was once in an entirely different appellation, probably Central Coast near the current position of Paso Robles.
Slippage like that along the San Andreas Fault today has been going on for a long, long time and the combination of ocean floor sliding under and northward slippage caused some unusual intrusions into the Franciscan. These intrusions were much more like the ocean floor, rich in Iron, Manganese, and Magnesium. Hydrothermal activity, pretty much like the Geysers today, leached Iron from the intrusions and injected it into the soil above leaving us the dark red to purple Iron rich soils of Hidden Ridge.
Iron makes blood red and it is part of the coloration of grape skins. Wine color comes from the skins. The unfailing color and phenolics of Hidden Ridge wine derive from this soil.
Valley soils have been washed down from many different rocks in the surrounding mountains. From the Santa Rosa side the Mayacamas Mountains begin with a wide band of relatively recent (we’re still talking millions of years) volcanic rocks called the Sonoma Volcanics. As one climbs out of Rincon Valley on the Calistoga road the Sonoma Volcanics are expressed as light colored tephra or tuffs that can easily be mistaken for limestone. This is volcanic ash, like Mt Saint Helens on steroids. Above these after the first bridge on the St Helena Road one finds buff colored ten million year old sandstones laid down when San Francisco Bay extended way up here. Only near the top of the Mayacamas Mountains where all the younger stuff has washed off does one find the Franciscan and Hidden Ridge.
In the valley bottom soils the red Iron has been diluted to brown and lighter buff colors from less Iron rich rock washed down after the dinosaurs left town.
Does purple dirt make an exceptional mountain cabernet? You bet it does. Here’s to the red blooded dinosaurs!

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