The Sonoma County Board of Supervisors gave final approval Tuesday to a mining operation that will extract up to 350,000 tons of gravel a year from a 6.5 mile stretch of the Russian River near Geyserville.

The project, by Napa-based Syar Industries, was given tentative approval by a 5-0 straw vote of the board in October. It was approved on a 4-0 vote on the consent calendar Tuesday. Supervisor Shirlee Zane abstained because her adult son has worked for Syar in its vineyard operations.

Syar plans to extract gravel over a 15-year period from 15 bars along the river, taking rock from above the water line from June 1 to Nov. 1.

Opponents, including the groups Russian Riverkeeper and Trout Unlimited, say the nearly 500 daily truck trips and additional industrial activity will irreversibly harm the Russian River, a key scenic and natural resource in the area.

But supporters and supervisors have pointed to the extensive mitigation efforts required to offset impacts to the riverbed, water quality, vegetation, wildlife and roads.

Opponents said they are considering a court challenge.