The Winemaker's Dance

Exploring Terroir in the Napa Valley

Jonathan Swinchatt and David G. Howell

Thank you for downloading this expanded tour of the geology of the Silverado Trail in California's Napa Valley wine country. This tour is based on a section of The Winemaker's Dance: Exploring Terroir in the Napa Valley, by Jonathan Swinchatt and David G. Howell, published by the University of California Press in 2004.

All material in this file is copyright (c) 2004 by the Regents of the University of California. The latest edition of this file can be downloaded, free of charge, at http://www.ucpress.edu/winemaker; it may be distributed to others but may not be altered.

Mile 1

Shortly after turning on to the Silverado Trail from highway 121, you will see a rocky ridge ahead. You are seeing the segment of the Vaca Mountains that rises up on the northeast side of the Stags Leap District. As you drive north, the first place to stop is the one-mile mark. The Silverado Trail bends left at Soda Canyon Road, to the northwest, and the view opens out. The ridge of the Vaca Mountains is on the right. To the left in the distance you can see the Mayacamas Mountains which form the western boundary of the Napa Valley. Notice the look of the valley floor. You are looking at the Napa Valley flood plain. The Napa River deposited the soil here over many centuries. The sediments that fill the valley were eroded from the sedimentary and volcanic rocks that form the bedrock of the Mayacamas and Vaca Mountains. The floodplain sediments are generally quite fine-grained, except for the river channel itself, which contains coarser material. As the river meanders back and forth across the valley floor, channel deposits mingle with floodplain sediments, forming a complex mix of fine and coarse layers.

Mile 2

As you approach the two-and-a-half-mile mark, look at the shape of the mountains that lie in the distance off to the right. These are the Vaca Mountains. The top segment of the Vaca ridge rises in elevation toward the North, ending in the steep slopes and gray cliffs that hang over the Stags Leap District. They formed when compression along the San Andreas Fault caused the rocks to buckle and break, stacking immense slices of one atop another. As the mountains rose, they grew so heavy that the layers could no longer hold together. They broke, along three great curving plains that now are reflected in three ridgelines in the Vacas. Great blocks of rock slowly slid westward down these slide surfaces. The rounded hills to your right are the remains of the lowest of these slides.

Composed entirely of Napa volcanics, the Vacas run all the way up the east side of the valley, culminating in Mount St. Helena, the highest peak in the region. On your right you can look at the rows of vines (at Clos du Val, for example) and notice how they curve gently upward as they intersect the base of the hills. These slopes are alluvial fans, accumulations of coarse debris washed from the hills. Vineyards also climb the lower, steeper slopes of the hills themselves, although the vines here are planted in material that is quite different from that found in the alluvial fans below. The vineyards on the upper slopes were developed before the enactment of stiff regulations that limit planting on hillsides with a slope greater than 5 percent. Now, out of concern for erosion and "visual pollution," environmental organizations are working to prevent further vineyard development in the hills, maintaining that the Napa Valley already has enough vineyards. The craggy cliffs that cap the ridge are made up of a variety of erosion-resistant volcanic rocks.

Mile 3

The three-mile mark offers a good view of the Mayacamas Mountains that form the western side of the Napa Valley. Unlike the Vaca Mountains, which consist at the surface entirely of volcanic rock, the Mayacamas are a bit more complex. Volcanic rock covers the surface in the northern third, ocean sediments of the Franciscan Formation in the middle third, and a combination of sands and shales of the Great Valley sequence and volcanic rocks is the southern third.

Mile 4

At the four-mile mark, the view to the right opens up and in the distance ahead, you will see the Stags Leap Palisades. The sheer cliffs got their name from a Native American legend about a stag being chased by a hunter. Instead of allowing itself to be killed, the stag leapt off the rocks to its death.

As you drive through this part of the valley, you can notice how the geography influences the winemaker's decisions about what to grow and how to grow it. On the left side of the road is the Napa Valley flood plain; on the right, the hills. Each has a different and characteristic substrate. Five thousand years ago, sea level was 300 feet lower than it is today; the Napa Valley was free of sediments and perhaps 250 feet deeper than it is now. As sea level rose, the Napa River built a flood plain. Water rushing from the hills carried sediments into the valley, depositing the coarsest material-boulders and cobbles-near the base of the slope and carrying the finer particles farther onto the valley floor. When you look at the hillsides on the right again, focus on the transition from hillside to valley floor. The substrate at the top of the transitional slopes tends to have the largest particles. Toward the bottom, the substrate tends to get finer and finer. The rate of movement of water through a particular substrate is determined by the size of the grains. Individual vineyards are "built" to take into account the availability of water, by choosing rootstocks appropriate for the moisture conditions, choosing grape varieties that are known to thrive in the particular substrate, and trellising and pruning to provide best access to the sun on that piece of land.

Mile 7

At the end of a long, straight stretch of road you will see Stag's Leap Wine Cellars on your right. This winery is home to SLV, the vineyard that produced the winning red wine at the 1976 Paris tasting-a pivotal event for Napa wines. The Fay Vineyard, directly north of SLV and also a part of Stag's Leap Wine Cellars, was the first Cabernet Sauvignon grown south of Rutherford when Nathan Fay planted it in 1961. Fay's wines influenced many Napa winemakers, including Warren Winiarski and John Kongsgaard. The caves at Stag's Leap Wine Cellars are dug into a volcanic plug, the remnants of one of the volcanic vents that fed the thick mass of Napa volcanics. Near the top of the hill ahead, you can see volcanic rock in the banks on both sides of the road.

As the road descends gently on the other side of the hill, Pine Ridge Winery appears on the left. Here the vines are planted mainly on sedimentary rocks of the Great Valley sequence. The high roadcut just past the winery entrance reveals the orange-red color of Great Valley sequence rocks that were baked by heat from the volcanic plug. Silverado Vineyards sits on the northern extension of the Pine Ridge knob. Where the road bends to the right, after the entrance to Silverado, a roadcut reveals layered sandstone and shale of the Great Valley sequence. Beyond this roadcut, the view opens up briefly on both sides. On the right, the vineyards of Shafer climb the steep hillsides at the northern end of the Stags Leap District. These slopes produce Shafer Hillside Select Cabernet Sauvignon, long considered one of Napa's finest wines.

From here, up to Oakville Crossroad several miles ahead, the Silverado Trail winds through a series of hills and knobs. As chapter 2 of The Winemaker's Dance explains, these unusual features are the toe deposits of a series of large displacements that formed after the Vaca Mountains were uplifted. In the distance to the west, on the left, arise the rugged and tree-covered Mayacamas Mountains, fronted by the long ridge of the Yountville Hills. These hills also formed as toe deposits of one of the large displacements. Highway 29 runs on the other side of the Yountville Hills.

Mile 8

Just south of Rector Reservoir, the road curves up a slight rise onto a straight, flat stretch. You are driving along the upper part of a small alluvial fan at the mouth of the Rector drainage. Paul Frank's Gemstone Vineyard lies at the southern end of this flat stretch. Frank designed the vineyard with the express purpose of growing grapes and making wine that would distinctly reflect the site. He planted Cabernet Sauvignon, Merlot, Cabernet Franc, and Petit Verdot, using types of rootstock and clones that he thought most suitable to the conditions. The wine has been very successful, but how well and in what way the wine reflects the site is more difficult to establish.

Mile 9

At the 9-mile point Rector Dam is visible on your right. This reservoir is built at the end of the Rector Canyon, a deep canyon cut in the Vaca Mountains. The mouth of this canyon is a small alluvial fan that stretches across the highway and off to the left. An alluvial fan forms at the mouth of the drainage where it leaves the mountains. Coarse sediment is dumped at the base of the slope, with finer sediment moving farther into the valley. Over time, changing stream positions deposit sediment in a fan-shaped pattern, much like an undersea delta.

The next vineyard on the left at 9.8 miles is Screaming Eagle, the source of one of the most expensive and sought-after wines in the valley. Screaming Eagle began as owner Jean Philips's homemade wine; word of mouth and the desire of many wine aficionados to be in on the most recent discovery quickly transformed it into a phenomenon. The wine is now made by star winemaker Heidi Peterson Barrett from perhaps 10 percent of the vineyard. Each year Barrett produces a mere 500 cases of Screaming Eagle Cabernet Sauvignon. This wine is only available through a mailing list at $250 a bottle and more. The rest of the grapes are sold to other producers.

Mile 10

After Screaming Eagle, the road bends to the right and you will soon see Joseph Phelps's Backus Vineyard at mile 10.3. The terraced lower portion is the original vineyard; the vines at the top, in downhill rows, were planted in 1999. There is also an upper section, out of sight from the road, planted on an extensive flat surface, that supports Dalla Valle, Showket, and Vine Cliff. For more than two decades Backus Cabernet Sauvignon has been one of the most consistently excellent wines in the valley.

Beyond Backus Vineyard, Oakville Crossroad intersects the Silverado Trail on the left. Rudd Wines occupies the land on both sides of this intersection. The original vineyard on the northern side of the intersection is developed on two types of substrate. The southern half lies on volcanics, as do the properties on the slopes above--Dalla Valle, Showket, Vine Cliff, Oakville Ranch, and Stagecoach Vineyards at the top of the Vaca Mountains. These properties are all related to the large landslides mentioned earlier. The northern half lies on a small alluvial fan. The fans of this side of the valley are much smaller than those on the west side.

Mile 12

As the road passes Rudd, it descends the northern flank of yet another alluvial fan, which formed at the mouth of a large drainage that cuts into the Vaca ridge a little north of Rector Canyon. Past Oakville Crossroad, the valley opens out to its widest extent. The road runs along the base of the eastern hills, up and down a series of rises and swales that represent older, uplifted alluvial fans. Looking directly to the left, you can see the short, relatively steep, upper slopes of these fans. Mumm Napa Valley lies near the crest of the largest of these features. Next, a series of small cuts at the side of the road display the mixed character of the alluvial fan sediments-boulders and cobbles lying in a matrix of sand and mud. To the left, you have a view of the heavily wooded Mayacamas Mountains across the valley, topped by the triangular peak of Mount St. John.

When you pass the 12-mile mark, a sign on the left announces the Beckstoffer Vineyards. This grower farms more than a thousand acres in the valley, selling most of the grapes.

Mile 13

ZD Winery and Mumm Winery both appear on your left. Keep an eye out for the roadcuts on your right. The exposed ground here is a great example of an uplifted alluvial fan. Rocks and boulders are randomly oriented in finer-grained material. At the 13.5-mile point, Highway 128 heads to the right. A short side trip up this road reveals outcrops of ocean floor sediment and ocean crust beside the road. Four tenths of a mile farther on is Rutherford Hill Road, which leads to Auberge de Soleil, the first exclusive resort to be built in the valley.

On the left lies the new Quintessa Winery and its associated vineyards. 180 acres of grapes grow on a unique piece of land, an elongate ridge at the edge of the valley. The Vaca Mountains to the east give grapes a western/late afternoon exposure to the sun; that is the time of day when air temperatures are highest. The Mayacamas Mountains to the west provide an eastern/morning exposure when air temperatures are lower. Winegrowers respond to these differences by utilizing all the various tools at their disposal-including choices of rootstock and clone, trellising and pruning decisions, irrigation plans, and careful attention to grape development and ripening. The series of hills and valleys at Quintessa expose the grapes to all the different angles of the sun, providing a diversity unusual for a single property.

Mile 14

At 14.5 miles, a tall roadcut appears on the right. The rock is volcanic ash, which makes up most of the rock along the road from here to just south of Calistoga. Note Taplin Road at 15.4 miles: turn right here for Joseph Phelps and, farther up the road, the Joseph Heitz Winery, which makes one of the benchmark Cabernets of the Napa Valley.

Once you pass Quintessa, a series of roadcuts reveal some of the volcanic rocks that make up the eastern hills. The road winds past these roadcuts for several miles. They are particularly well exposed at Taplin Road and along a stretch south of Deer Park Road. In many of them, the beds, composed mainly of volcanic ash, are nearly vertical, tilted by the forces that formed the Vaca Mountains. These exposures of volcanic rocks are interrupted only at Deer Park Road, where the rounded pebbles and cobbles of an older, uplifted alluvial fan can be seen in a road bank south of the intersection.

Mile 15

At 15.7 miles you will see a small collection of houses and buildings--new farm-worker housing. The economics of wine in the Napa Valley requires a good supply of inexpensive labor to work the fields. Housing for a seasonal labor force, used during harvest, has long been a problem in Napa. This housing is one of the ways the problem is beginning to be addressed.

Mile 16

At 16.9 miles is Howell Mt. Road, and just beyond it the vineyards of Napa Valley Reserve. Here, subscribers assist in vineyard management, harvest, and winemaking, thus being able to participate without the worries and pressures of winery ownership.

Mile 18

From Deer Park Road (mile 18.5), you can visit the town of Angwin, Pacific Union College, and the Howell Mountain AVA. At the intersection, you can see the remains of an older alluvial fan that has been slightly uplifted as the mountains have risen. The Howell Mountain AVA is underlain by volcanic bedrock. The substrate and climate here produce wines that are intense and powerfully tannic when young but can age with exceptional grace.

Mile 19

North of Deer Park Road, Lodi Lane is the next place to pause at 19.3 miles. Duckhorn Vineyards are on the left; on the right you can see a massive outcrop of beds of volcanic ash with pods and layers of obsidian. Obsidian, a shiny black, glassy-looking rock that forms when some types of lava cool very quickly, is the material that gave Glass Mountain its name. Obsidian identical to this lies also on the west side of the Mayacamas Mountains in Sonoma County. First deposited by streams, this material was transported to its present position by movement along the system of geologic faults that cut through this region. Collectors of the black volcanic glass have dug holes in this outcrop. Native Americans used obsidian for the heads of spears and arrows. The ground surface of Chabot Vineyard, owned by Beringer and located up Glass Mountain Road, is awash with glistening fragments of obsidian.

Mile 20

Opposite the entrance to Rombauer Vineyards, one of the most colorful and interesting roadcuts in the valley appears. Thin layers of volcanic tuff and obsidian top a bright orange, rubbly rock that probably represents a soil zone baked by the heat of the volcanic ash as it accumulated on the surface.

Mile 21

If you are traveling in the fall, just past Crystal Springs Road (mile 21.1) a vineyard on the left provides a splash of brilliant red in a valley otherwise covered by the yellow leaves of grapevines at this season. The color comes with leaf roller disease, a condition that affects grape yields but not quality.

Mile 22

Passing mile 22, the stark white Sterling Winery appears at the top of a hill to your left. You are now driving over a large alluvial fan coming out of Dutch Henry Canyon to your right. Three tenths of a mile down the road the three palms off to your left are the symbol for the aptly named Three Palms Vineyard. Anecdotal evidence suggests that this area contains the hottest spot in the valley, nestled in a small nook at the base of the Vaca Mountains.

The road continues on to Calistoga, winding through the edges of the hills and along a wider flat at the mouths of Simmons Creek and Jericho Canyon. Eisele Vineyard, on Pickett Road, was originally planted by Milton and Barbara Eisele and is now part of Araujo Estate. It has produced widely acclaimed Cabernet Sauvignon, made by a variety of winemakers, over its history of more than three decades. During the 1970s and 1980s, much of the fruit went to Joseph Phelps Winery for its Eisele Vineyard Cabernet Sauvignon, made by Craig Williams. After Bart and Daphne Araujo bought the vineyard, Tony Soter became the winemaker for some years during the early 1990s. Françoise Peschon now makes the wine, with Michel Rolland as consultant.

The hot springs of Calistoga-remnants of the relatively recent volcanic activity-have attracted visitors since the middle of the nineteenth century. Today, the area of potential volcanic activity centers on the region of Clear Lake, a few miles to the north. As you approach Calistoga, Mount St. Helena rises to the north of the town, providing a suitably majestic backdrop for this narrow northern end of the Napa Valley.