A torrent of rain battered West Marin last week, washing out roads, triggering mudslides and causing flash floods. After four days of steady downpours, the brunt of the storm arrived on Tuesday, as an atmospheric river—a narrow band of moisture propelled by powerful winds—swept across the region. The National Weather Service recorded nearly five inches of rainfall in Point Reyes Station over a 24-hour period, on top of the 4-plus inches that had fallen earlier…