Between two of the most beautiful towns on the California coast, Carmel-by-the-Sea and Big Sur, there’s a hidden valley: 31 square miles shared by just 300 families, each of whom owns a small parcel and the right to build. The area, originally known as Rancho San Carlos, was one of the last intact Mexican land-grant ranchos in California. Now it’s the Santa Lucia Preserve, a private eco-park, off-limits and unknown even to area natives.

San Francisco architect Eric Haesloop discovered the preserve through his clients Bob and Allyson Kavner, who own five acres there. “It’s so spectacular,” he says, “just what you imagine California was like a hundred years ago, with wild boars, turkeys, and birds galore.”

The Kavners’ lot is situated where the oak woodlands of the coastal mountain range meet the meadows of the valley. An early farmhouse for the ranchero once stood here, surrounded by a few scattered fruit trees. Surveying the site, Haesloop realized that there was a lot of history, both natural and human, that the architecture would need to respond to—–not to mention the needs and desires of the Kavners themselves. Both husband and wife are originally from the East Coast and have many happy memories of summer vacations spent in upstate New York. They fantasized about an Adirondack-style camp, complete with cabins, to better host their four grown children and five grandchildren. The house was to be a weekend retreat, a place to escape the pressures of work. Bob Kavner was an early president of Idealab, the high-tech incubator, and now serves on the boards of several successful Idealab start-up companies. Weekends, however, are devoted to his hobby, woodworking. “How do you bring in those memories and that love of traditional wood construction,” asks Haesloop, “with the Northern California climate, topography, and building traditions?”

The answer turned out to hinge on a building technique called PISE (pronounced “pee-zay”), an acronym for “pneumatically impacted stabilized earth.” The technique is a modern method of handling one of the oldest known building materials: dirt. It’s akin to adobe or rammed-earth construction and results in walls that are up to two feet thick, never need to be painted, and instantly look like they’ve been around forever.

The Adirondack style that the Kavners remember so fondly is a rustic American take on the Tudor mansion or Alpine chalet, with giant log columns used in place of milled timbers. A log column holding up the roof typically has its branches left on it, functioning as natural struts and beams. Smaller twigs and branches provide decorative details. An Adirondack camp lodge looks like a log cabin, supersized and fit for a king, but the drama of the style conceals a practical side: It was a way for lodges of monumental scale to be built in the remote mountains because materials—–in this case trees—–could be harvested from the site.

Haesloop’s firm, Turnbull Griffin Haesloop, is noted for helping pioneer an architectural approach distinctive to the San Francisco Bay Area: the Sea Ranch style, a form of rural modernism that eschews the rectangles and steel of the International Style for simple, shedlike forms and unpainted wood left to weather naturally. While designing the Kavner house, Haesloop realized that PISE walls were the key to bridging the Adirondack and Sea Ranch styles and giving the Kavners the house they were looking for. Thick earthwork walls would give the main house the drama of something much larger, like a mountain lodge, but also subtly refer to the early architecture of California, the Spanish mission.

Even more important, using PISE is one of the greenest ways to build, and thus it appealed to a desire of both the Kavners and Haesloop to tread lightly on the land. The house was sited in the shade of the forest, its main view framing a particularly grand oak, so active solar systems on the roof were ruled out. But PISE’s mass turns out to be the perfect passive solar strategy to deal with the preserve’s distinctive climate pattern of hot days and cool nights. “PISE is essentially on a shifted schedule, absorbing heat in the day and radiating it at night,” explains Haesloop. “It acts as a thermal flywheel.” In addition, the earth for the walls could be taken from the debris pile created by digging the house’s foundation, making construction close to carbon-neutral.

Haesloop and his partner Mary Griffin designed the house around a large, barnlike wood-and-glass pavilion, buttressed on each side by PISE sheds. Inside is a free-flowing open-plan layout with a living-dining room on one side and a library on the other. Upstairs are two modest bedrooms and bathrooms. Throughout, the massive PISE walls provide a counterpoint to the reclaimed wooden beams and peeled-cedar log posts. There’s wood everywhere: paneled walls, wide-plank barn-wood floors, two staircases made from huge piles of stacked lumber—–all of it reclaimed or certified sustainable.

Less obvious, but no less prevalent, are other passive solar touches: strategically placed high windows that open to let out hot air; fans on the porch making the outdoors comfortable on even the hottest, buggiest summer days; and plenty of cross ventilation. They’re small elements, but they add up to a house that doesn’t need air-conditioning, usually mandatory in the preserve’s hot microclimate. Up the hill behind the house, two small guest houses are tucked into the forest, an arrangement that echoes the lodge-and-cabin placement of the Adirondack camp style. What’s more, the setup allows the Kavners’ main house to be quite compact, requiring less energy use when they’re on their own.

When asked what she likes most about the house, Allyson says simply, “What you see is what you get,” and then ticks off a number of examples. The zinc roof was deliberately left unpainted, so that water runs off clear. The log columns are not decorative details (though they fit the style); they actually hold up the roof. And then there is her favorite aspect of the house: the PISE hearth, chimney, and walls. In the construction phase the neighbors would invariably ask what color she was going to paint them, but in Allyson’s view paint would be a shame. To her, PISE’s natural dun color is “exquisite”—–a reflection of its earthen origins and a reminder of the intention behind the home’s design. “I wanted the house to complement the land,” she says, “to be subservient, rather than stand up and wave and show the world how big and beautiful it was.” And surveying the results contentedly, “I wanted it to fit in.”