Marin County Fire is planning to conduct a controlled burn in the Mount Tamalpais watershed as early as next week, after wet weather postponed previous attempts to rid the watershed of overgrown vegetation that can fuel wildfires. The burn will eliminate 27 acres of vegetation between Stinson Beach and Mill Valley, creating a firebreak. Chief Todd Overshiner, a spokesman for Marin Fire, said about 25 of the department’s firefighters would participate in the burn, which…