An expansion of Mark West Quarry east of Santa Rosa earned final approval this week after county supervisors required additional road improvements on its busy haul route.

The requirements are meant to enhance safety for motorists and cyclists on the narrow Mark West Creek and Porter Creek roads.

BoDean Co., which has operated the 103-year-old quarry since 1989, is set to do some road-widening, pullout and striping work, install signs and make a financial contribution toward future county improvements on the corridor. Combined, the measures are worth $570,000.

The Board of Supervisors included the extra requirements this week when it unanimously signed off on a 20-year permit allowing the quarry to expand into an adjacent property.

The formal go-ahead came after a board hearing last month raised questions about the few traffic safety improvements being required of the project.

The expansion could add 37 to 59 truck trips a day on the east-west route — an increase the county described as "substantial" in an environmental impact report.

The only major modification endorsed last month with the project was a $255,000 contribution to a future traffic signal at Riebli Road.

County planners did not recommend a major roadway overhaul, including widening on about 5.5 miles of road, because the county can't afford its $26 million share of the project. BoDean also balked at its $8.6 million share.

Instead, the company will do work — or make a payment toward county work — for road widening on a total of about 3.4 miles of the route. It will stripe and sign another 3.4 miles to create class II bike lanes, widen and pave about a half mile of turnouts and install four bicycle-activated flashing beacons and signs at the narrowest sections of roadway.

County planning officials said they understood BoDean planned to begin immediate work on the expansion. Bill Williams, the company's general manager, could not be reached for comment Thursday.

(You can reach Staff Writer Brett Wilkison at 521-5295 or