A nodule of Napa Glass Mountain obsidian, etched by hydration during its long burial, reveals signs of its origin as a thick, sticky lava. Photos by Andrew Alden

The Napa Valley is an intriguing place even if wine doesn't interest you. Its very geography has an intangible personality. Running north-south, the valley is lit differently throughout the course of the day. It has the flat valley floor along the Napa River that you'd expect in a major agricultural region, but odd rocky hills are scattered about the valley with the irregularity of tossed pebbles. On behalf of Napa Valley winegrowers, geologists have studied the underlying soils and rocks, tracing from them a history of tectonic upheaval, recent volcanism and gigantic landslides.

The western side of the valley is the Mayacamas Mountains, here made up largely of marine sedimentary rocks of the Franciscan and Great Valley complexes (100 to 150 million years old). The eastern side is the Vaca Mountains, which consists mostly of much younger lavas of the Sonoma Volcanics (less than 5 m.y.). Here it is in a simplified geologic map.

The valley floor consists of recent sediments (Q) while young volcanics (T) and older sedimentary rocks line its sides. From USGS Scientific Investigations Map 2956.

Each set of rocks responds its own way to California climate and yields its own set of soils, and the floodplain between them mixes the two in different blends. Its wide range of soils and settings is part of what makes the Napa Valley such an endless playground for winegrowers. The same was true in prehistoric times, when the valley was a rich habitat for the Wappo and Patwin tribes and other peoples before them.

And this brings us to Napa Glass Mountain.

The natives made their cutting and scraping tools as needed, chipping them from stone of a few select kinds. The best toolstone is obsidian—a glasslike lava without crystals or bubbles that would mar the sharp edges and flat faces of an effective tool.

Obsidian is uncommon. To make it, a lava must have both a very high silica content and a low water content; it also helps to cool quickly. High-silica lava is classified as rhyolite and the Sonoma Volcanics field has plenty, but few rhyolites yield obsidian. Notable sources for the natives in this part of California were Annadel near Santa Rosa, Borax Lake near Clear Lake, and Napa Glass Mountain, which is just north of the town of St. Helena. Toolstone was an important trade item, and archaeologists map its distribution in ancient sites as clues to prehistoric commerce.

The Napa obsidian is a stone of a luscious pure black, and you can see it in a large roadcut on the Silverado Trail north of St. Helena at the narrowest point of the Napa River's floodplain. Here's a closeup geologic map.

Pinkish units are part of the Sonoma Volcanics (Tsa, Tsr, etc.), gray units are Franciscan rocks, units with "Q" are recent sediments. From USGS Scientific Investigations Map 2956.

The roadcut is just north of the intersection with Lodi Lane; you can park on either side of the road but be careful of traffic. The exposure is tall and shows the crude bedding of the mixed ash and lava beds, now highly weathered.

Obsidian occurs scattered in a whitish matrix in fractured lumps up to a meter long. The matrix may be altered material that was once obsidian, and/or it may consist of fine rhyolite ash—I have not studied it closely enough to hazard a guess. Parts of it may actually be perlite, a lightweight stone that forms where rhyolite reacts with internal water. Obsidian does not last long in the geologic record because its crystal-free substance is prone to attack by chemical weathering.

You don't need to dig into the cliffs; let other people who actually use obsidian do that risky operation. Instead, poke around your feet and look for bits like these.

The outsides are rough and coated with white hydration rinds, but inside they display their creamy texture and lustrous conchoidal fracture, the properties that make obsidian the ideal toolstone. Don't be greedy. And be ready to tell passers-by, like the curious police officer I spoke to during my last visit, what this cool place is all about.

More:
Obsidian photo gallery
Perlite
Rhyolite
Stone Tools

Each big storm with a high tide and an
onshore wind takes a big bite out of Sarichef.Photo By Shishmaref Erosion and Relocation Coalition

In an email this week from John Woodward, an Alaska builder and Home Energy author, he wrote, "I put together a working/management group to manage the relocation of the community of Shishmaref sustainabely. They live on Sarichef, a barrier island that global warming is wiping out."

Shishmaref is home to a small community of Inupiat, a Native American tribe. John is working with the Inupiat Tribal Government, the City of Shishmaref, and the Shishmaref Erosion & Relocation Coalition, to salvage as much of the village as possible before it goes under water and move it, along with the island inhabitants, to a new plot of land in the interior of Alaska.

The Army Corp of Engineers gives the island about 5 or 10 more years of livability. But as the ocean and permafrost warm and the ocean rises, unpredictable storms take a heavy toll on the island. "Each big storm with a high tide and an on-shore wind takes a big bite out of Sarichef," says Woodward.

The community is seeking funds for a comprehensive alternative energy plan, an anaerobic pump/methane generator, and the retrofit of all existing buildings, including more than 110 homes, community buildings and a school. The homes will be retrofit to use less than 5 Btu per square foot to heat. Heating load calculations can be pretty complicated, but in general, contractors recommend furnaces that can provide 30-50 Btu per square foot to heat homes in the Bay Area. To reach such a high level of energy efficiency, the Shishmaref homes will have the insulation installed on the outside of the structure, a technique that Woodward has successfully used in the past. The new village will have the look and functionality of the Inupiat culture as defined and designed through community planning.

"Our community planning process involves community charettes with the whole community gathered in the school gym," say Woodward. "The goal of these meetings is the rough-out of a comprehensive community plan for sustainable relocation of the existing salvageable infrastructure and the development of the new village site."

The Inupiat will build their new village to suit their needs and lifestyles, to be efficient, and to be in harmony with its surroundings-in other words, sustainabely. Let's keep an eye on our northern neighbors, who may teach us some valuable lessons. How long before whole towns in California will have to relocate because of water shortages? We all witnessed what happened in New Orleans a few years ago. How long before towns and cities on the coast of California will have to move inland or be seriously reconfigured because of the rising Pacific Ocean?

You can e-mail John Woodward with questions, comments, ideas, and offers of help at panuktuk@yahoo.com.

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