 From various points in Arlington, the Olympic Mountains,
Mount Pilchuck, and Mount Rainier are visible on the horizon.The Stillaguamish River valley and floodplain, including Arlington, lies in a lahar hazard zone downstream from Glacier Peak, an active stratovolcano in the eastern part of the county.During an eruption 13,000 years ago, several eruption-generated lahars deposited more than of sediment on modern-day Arlington.