The egg industry has returned to Sonoma County with a scale and a level of mechanization that its early pioneers would scarcely recognize.

A half century ago, some 2,700 egg farmers lived between Eureka and the Golden Gate. Today, just two Sonoma County farming families are approaching the same output of the industry during its good years, though not yet at its heyday, said Petaluma-based egg farmer Arnie Riebli.

The operations are doing it with fewer hens and with warehouses equipped to feed the birds, collect the eggs and remove the manure with little human labor.

Riebli, 67, a self-described "hard-nosed country farmer," is the owner of Sunrise Farms, the county's largest egg producer at a million eggs a day.

Two warehouses on one of his ranches west of Windsor illustrate the extent of his operation. One building contained 135,000 caged chickens, a practice that would be banned under Proposition 2 on the November ballot. The other housed 25,000 cage-free chickens.

The cage-free birds are allowed to move onto a floor covered with rice hulls and chicken manure. They also can sit on perches on two upper levels or use a daytime nesting area curtained off by vinyl screens.

In the other warehouses, the birds remain in their cages all day. The feed is dispensed on one side of the cage and water on the other, a design that Riebli says prevents any animal from hogging all the food.

Three workers care for the ranch's 400,000 caged birds, Riebli said. In contrast, one worker is needed to watch over the 25,000 cage-free birds.

The county's chicken boom dates back more 120 years with the development in Petaluma of an egg incubator. In the 1940s, the city counted three dozen commercial hatcheries and in 1945 the county's chicken ranches produced 51 million dozen eggs, a record never surpassed.

Over the next five decades the industry experienced a slow, steady decline. By 1993, the county released its last count of egg production, nearly 14.6 million dozen.

Six years ago, Riebli, who grew up in the county on a combined dairy and chicken ranch, with his family began consolidating operations in Sonoma from three other counties. He estimated that the county's output now approaches 1.3 million eggs a day, nearly 40 million dozen eggs a year. That level of production hasn't been seen in the county for almost 50 years.

He said his company does about $40 million a year in sales, 90 percent of which are to stores within 65 miles of Petaluma. He also has sold eggs to Russia, South Korea and the South Pacific and three times a week his eggs are packed in containers on ships bound for Hawaii.

He said he treats his chickens with vaccines but never antibiotics.

"If you mistreat them," he said, "they won't produce."

Steve Mahrt, part of the county's other family with a substantial egg business, declined to give out production numbers.

Mahrt has raised cage-free chickens for 25 years. When he first proposed such a business, he said, "my dad laughed at me." His father still keeps his hens in cages.

Both Mahrt and Riebli said their industry is willing to produce more cage-free eggs if consumers are willing to pay for the extra effort. On Thursday, the difference at the Fourth Street Safeway was a dollar a dozen -- $2.79 versus $3.79 -- between regular and cage-free Lucerne AA eggs.

Nonetheless, Mahrt noted that in 25 years the cage-free egg business has grown to account for only 5 percent of the total market.

"So what's that tell you?" he asked. "It's growing but not that fast."