San Bruno Mountain stands over Visitacion Valley like a weather report — when its shoulder is clear, it is a mowing day. Quality Lawn Care L.L.C. cuts and keeps lawns on those blocks above Bayshore, where the Greenway climbs in garden steps and the yards are level and generous. The wind finds the gap in the afternoon, so the work goes early and the clippings go straight into the bag. Trimming around fence posts and mailbox stands is the small part of the job that people notice most. After a storm the whole valley turns emerald, and the calendar fills up on its own.