In the face of strong concerns from activists, neighbors and Fish and Wildlife officials, the Marin County Planning Commission on Monday unanimously upheld plans for a new three-story home on a lot prone to landslides above Woodacre Creek. 

The approval followed hints of a lawsuit from the Salmon Protection and Watershed Network, which said the county should complete a court-ordered cumulative environmental impact study on development in the San Geronimo Valley before green-lighting the home;…