Mark West Quarry in the hills between Santa Rosa and Calistoga is asking Sonoma County supervisors for permission to expand to a neighboring property, but owners say it will not represent a major increase in the volume of rock being mined.

The century-old quarry already has permission to annually mine up to 500,000 cubic yards, or about 750,000 tons, of hard rock known as aggregate, highly prized as the base for roads, building foundations and other construction projects. The quarry had been digging steadily northward on the 87-acre property until it began to hit an unexpected patch of volcanic rock that is not useful for gravel and other rock products.

The proposed expansion, on a 33-acre site to the west, will allow the Porter Creek Road quarry to follow the harder rock that it has been mining since 1910, said county planner Sigrid Swedenborg.

"They want to move west so they can stay in the same strata," she said.

The maximum volume of rock coming out of the quarry will not change under the proposal, which will come before the supervisors on Tuesday, Nov. 5, she said. The owner, BoDean Co. of Santa Rosa, is asking the board of supervisors to rezone the new property for mining and grant a 20-year use permit to dig there.

Some neighbors are crying foul, raising concerns about noise, views and a likely increase in truck traffic on the narrow and winding roads on the mountain.

"The county really hasn't looked at the impact on everyone here in our forest and our neighborhood," said Janet Angell, operator of the nearby Petrified Forest, a private tourist attraction that features well-preserved redwoods and other fossilized trees that are more than 3 million years old.

When the matter came before the county planning commission in September, Angell complained that the removal of the trees on the new site would damage wildlife and scenic views and would harm the rural character of the area, which is protected by a county plan for the Franz Valley area.

The consultants preparing the environmental impact report on the project, however, said they found no inconsistency with the Franz Valley plan.

Angell and other residents also raised alarms about the portions of the environmental impact report dealing with traffic, showing that the quarry might add between 37 and 59 trips per day by heavy gravel trucks headed west toward Highway 101 on Porter Creek Road or east toward Calistoga on Petrified Forest Road.

"The imposition of expansion will only intensify a very dangerous situation," wrote neighbor Anita Salas in objecting to the plan.

But Swedenborg said the report's figures are misleading, since they are compared just with truck traffic in recent years, which has been depressed because of the economic downturn. The figures in the report reflect traffic much like it was before the downturn and is consistent with the maximum amount of rock the quarry is already permitted to ship out.

The report outlines a series of measures, including widening portions of the Porter Creek/Mark West Springs Road toward Santa Rosa and adjusting the intersections in Santa Rosa and Calistoga that could ease the traffic congestion. Widening the road into Santa Rosa alone, however, could cost more than $30 million, and the report calls on the quarry to pick up roughly a quarter of the cost of eventual widening the road.

East Bay developer Mike Vranjes said he had planned to develop a number of large nearby forested lots into homes, but the new quarry will be visible from two prime hilltop sites.

"Now they're looking down into a quarry," he said, adding he's decided to sell the entire project in part because of the quarry expansion.

He also said the the environmental report did little to reassure him that the mining would not affect the wells that would supply the lots.

The report, however, calls on the quarry to plant trees to screen the work, and hide a large solar array that powers the operation, within five years. It calls for extensive monitoring of area wells and waterways to ensure the mining does not affect water quality or quantity.

Planning commissioners agreed with the consultants who prepared the environmental report, who concluded that the project doesn't pose a significant threat to the area, at least with some mitigation measures outlined in the report. The five-member commission approved the project unanimously on Sept. 26.

Representatives for BoDean did not return a call for comment, but the company has consistently said its expansion will not greatly affect the area. Any increase in traffic or other problems are more than offset by the benefits of having a working gravel mine in the area as an alternative to dredging rivers for rock, a traditional practice that has heavily damaged spawning grounds for salmon and trout all along the North Coast, said the company and county planners.

"We have done everything that we can to be good operators and stewards of the land and operate in a sound way," said owner Dean Soiland, who bought the quarry in 1989, at a June public hearing. "It's been a great experience for the most part and I think we have had a good relationship with the county and neighbors and we want that to continue."

You can reach Staff Writer Sean Scully at 521-5313 or sean.scully@pressdemocrat.com.