James Conaway, the bad boy author whose two Napa Valley books have laid bare local political wars and the vanities of wealthy wine industry newcomers, is back.

The author of “Napa: The Story of an American Eden” and “The Far Side of Eden” returned Thursday morning to address a California Preservation Foundation conference at the Napa Valley Opera House.

Repeating criticisms found in his books, Conaway said the undoing of the Napa Valley may be the sprawl of boutique wineries by rich newcomers who would sacrifice our natural and architectural heritage in the name of “showing off.”

Because of its international reputation, the Napa Valley is attracting a swarm of millionaires who build “baronial” estates and gut the integrity of neighborhoods by buying second homes, Conaway said.

He cited the architecture of Dominus Estate — a winery covered with stone-filled gabion enclosures — as an example of “totalitarian” design, an “unapproachable” building that serves the “vineyard elite” that now rule the Napa Valley.

In the same vein, Conaway disparaged the Frank Gehry-design for what will be Hall Winery in St. Helena, a clear case of a building dictated by “fashion, not function.”

Tourists play into this trend, Conaway said. “They’re attracted by the spectacular.” Be wary of catering to tourists, he said. “Tourism can devour the thing it loves.”

Conaway, who is an editor at large for Preservation magazine, said George Yount, the valley’s first white settler, would hardly recognize the place today.

The Napa of his day was marked by abundant wildlife, clear-running streams and dense forests on the western hills, Conaway said. If conference attendees were to venture into the hills today, they would find forest “scrapped raw” by vineyard development, he said.

Conaway praised the wine industry as the essential underpinning for the Napa Valley’s quality of life. “Agriculture is the source of all good things here, although it’s easy to forget sometimes,” he said.

Perversely, the very success of the Napa Valley wine industry — wine grapes are “one of the most valuable legal crops in the country” — has created the conditions that threaten it, he said.

The valley is attracting the mega-wealthy who want a piece of the action, he said. Vineyards have been planted on questionable terrain. The homes of the rich are infected by “gigantism.”

Corporations, which now own 20 percent of the valley’s tillable land, are another threat, Conaway said. In a wine industry downturn, corporate owners might be tempted to spend big bucks to repeal the Agricultural Preserve, allowing vineyards to be replaced by houses, he said.

Conaway lamented what he sees as the prevailing ethics of the times. Americans value growth and land use entitlements more than preserving our country’s architectural heritage and landscapes, he said.

“No piece of the nation goes unassigned to market forces,” Conaway said.

Conaway’s next book, set for release later this year, is “Vanishing America: In Pursuit of Our Elusive Landscapes.”

For those who want Conaway’s take on Napa Valley happenings since “The Far Side of Eden” came out in 2002, stay tuned. He’s working on the third volume of his Napa trilogy.