There is a river under Yonkers. The Saw Mill runs beneath the old downtown and steps back into daylight at Van der Donck Park, and this city has always been built around water it cannot quite see. Ahoqui Lawn Care, Inc. works the surface of that ground the whole year — mowing and trimming through the green months, plowing driveways and clearing walks when storms push up the valley. Summer mornings begin before Nepperhan Avenue fills; winter mornings begin earlier still, headlights and a blade. What gets left behind is simple and complete: a lawn with a clean border, a driveway with a straight edge, salt on the steps.