Pisoni Vineyards from Below:
A Short History of Monterey County’s Geology

The foothills of the Santa Lucia Highlands, bask in a brief moment of sun.

Wine is often described in terms of its minerality, and winemakers are quick to consider the role soil composition plays in grape-growing. But we don’t often consider the rocks whose slow shifts and changes across the eons have played their own part in supporting the complex amalgam of compounds in the earth that lies above them. At Pisoni, we work in accord with the yearly cycle of the seasons. But we also like to take the long view of the land that sustains us. In the piece that follows, we approach our vineyards from Earth’s time rather than our own. We hope you enjoy this geological journey through the region we love.

The rocks below what John Steinbeck called in East of Eden “the thin flinty soil” around Salinas have been around a long time. How long? Cast your mind back twenty-thousand years ago to the time when the ancestors of California’s present-day Ohlone peoples settled by Monterey Bay to hunt and fish after walking across the land bridge over the Bering Strait. Then unspool the thread of time a hundred times this length, to the Miocene Epoch (named by nineteenth-century British geologist Charles Lyell) some 23 million years back when mammals came to be. Now toss the line ten times farther than you just unspooled it, to find yourself in the middle of the Jurassic Period when dinosaurs strode the Earth and the first flowering plants opened colors to the sun our sky had never seen. From this point, extend the line of time some fifty more million years more, and you’ll find yourself in the Paleozoic.

Sometime during the Paleozoic Epoch, when Earth was some two billion years old (a little less than half the age it is now) and insects and fish were the only sentient life, the stone that lies below the rocky soils of the Santa Lucia Highlands where our vineyards are located solidified slowly from molten material underneath the crust. Named by geologists for the Salinas Valley running below the highlands, the Salinian Block is composed largely of granite—the very same substance the drills Gary used on Pisoni land to locate a wellsite bore into after they tunneled through several feet of soil on the surface where grapes would eventually seed and fruit. The core of the Salinian block is made up of fragments of batholith intrusions, material that welled up from the mantle as magma through metamorphic rock—mainly schist and gneiss—and which is even older. Cooling solidified this material in the form of granite, and faulting cracked and folded it under the rising slopes of the Sierra Nevada. If you wanted to travel down to the tip of one of these broken-up granite batholiths, you would need to descend some six to nine miles below the surface hikers walk—as far a distance below ground as planes fly when they cruise above Earth’s surface. But the world’s most sophisticated equipment, working for months on the Japanese drilling ship Chikyu, has only plumbed about a mile of Earth’s crust. To dig deeper, you’ll need your imagination.

The geology of Monterey County
A rare cutaway of Monterey County’s geology; detailing the current and prehistoric past of this region.

Our land on the Santa Lucia Highlands sits atop alluvial fans, fan-like deposits of sediment that spread out on valley floors below fast-flowing mountain streams. In our case, these fans are composed of the igneous granite that makes up the Salinian Block as well as the bands of schist and gneiss produced at very high temperatures.

By contrast, the materials that make up the Franciscan complex distributed throughout the California coast ranges and the San Francisco Peninsula is less ancient. Much of this material, churned and mixed as if with a blender by the movements of tectonic plates, formed during the Cretaceous Period and the late Jurassic. It, too is composed of metamorphic rock, but contains far less granite and more chert, serpentine, and greenstone—materials metamorphosed under pressure from rock that is oceanic in origin.

A close look at an interlay of rocks and gravel soils on Pisoni Vineyards.

The Salinian Block and the Franciscan Complex are different structures. Yet both developed out of the relationship between three tectonic plates: the Pacific, the North American, and the Farallon. (Consider how much energy, in the form of heat, you give off when you rub your hands together quickly. Now, think of the hard, brittle sections of the Pacific and the North American plates gliding above Earth’s mantle as giant hands pressing and sliding alongside one another, and imagine how much stress is created.) The Farallon, an oceanic plate like the Pacific, slowly got pushed underneath the North American plate and is lost to us now. But when coal swamps were first laid down and insects invented themselves, it was sandwiched between the Pacific and the North American plates. Later, during the Jurassic Period, the two larger plates began to converge, and the Farallon slipped (subducted, geologists say) under the North American. At the area where the Farallon began to dive underneath the North American plate, there was a great deal of friction, which ripped off pieces of both plates. This subduction zone, created from the press of two opposing sides, was put under great stress. (Imagine that you’ve cupped a substance like bread or cereal or even a chocolate chip cookie between your hands. When you rub them together, that substance gets heated and twisted and broken—and your hands become a sticky mess.) Just so, the rock caught betwixt and between the two plates was churned and turned and melded by the pressure into metamorphic material. (This pressure continues to exist today: after the plates switched from pushing against each other to slipping past each other in parallel, they created what we know as the area through which the San Andreas fault runs.) Most of the Farallon was pushed miles below the surface into Earth’s mantle ten million or more years ago. But the diverse material at the area where it began to slip under the North American plate eighty million years before that remains. This diverse material, chemically changed through the process of metamorphosis, comprises the Franciscan complex.

The Salinian Block which forms the basis of the rock underneath the soils of the Santa Lucia Highlands is not only older than the Franciscan assemblage, but an immigrant of sorts.

The Salinian Block which forms the basis of the rock underneath the soils of the Santa Lucia Highlands is not only older than the Franciscan assemblage, but an immigrant of sorts. It originates far to the South, around the area where the Sierra Nevada was formed. Birthed during the Paleozoic, the mostly granitic material of this block was pushed and pulled and tugged by transform faulting along the contact zone where the two plates slid past each other in the area that became the San Andreas fault zone. This faulting torqued and split the Sierra Nevada batholith, cutting slivers of its mass off and moving them north and west to their current placement, which runs from the area around Bodega Bay south to Mount Pinos in the Los Padres National Forest.

Geologic map of California
The overview of California’s dynamic geology. Observing the granite-based rocks (indicated in red), one can see the path they had taken from Southern California to where they were been pushed and dragged up through the coastal range and all they way to Point Reyes.

Some 140,000 years ago, the San Andreas and its eastern neighbor, the San Gregorio, began to slide against each other very rapidly. The rapid movement uplifted slabs of the Salinian into the Santa Lucia Range. Granite is a buoyant rock; rather than be sliced to ribbons, this section of the Salinian rose wholescale with the action of the two faults. As a result, the Santa Lucias, while set next to the coast, are mostly composed of granite. Their rapid formation encouraged equally rapid soil deposition. That is, the steep slopes, which were uplifted with more verticality than the Gabilan range east of the Salinas Valley, eroded very quickly. The granitic sediments they sloughed off and which ran toward the valley collected in the alluvial fans of the highlands. Alluvial fans such as these are rich in nutrients and very well-drained.

Here, in this foggy, windswept place, our vineyards are located. Climatic changes that occurred after their initial formation have introduced even more complexity to the rock of this region. During the end of the last ice age, the ocean crept further inland and laid marine sediments atop the coarser soils eroded from the peaks. It turns out that the “thin flinty soil” Steinbeck wrote of in East of Eden is made of stronger stuff than he supposed. Composed of schist and gneiss, it is full of granite but laced with marine materials. At Pisoni we work hard to create wine that possesses complexity. But it is the complex materials created by Earth’s enduring labor that make all our efforts possible.

 

Written by Anne Goldman

http://annegoldmanwriter.com/