 Arlington's city limits are generally defined to the south by Marysville at State Route 531 (172nd Street NE) and roughly 165th Street NE, to the west by Interstate 5, to the north by the Stillaguamish River valley, and to the east by the Cascade Range foothills.The city's urban growth boundary includes within and outside of city limits.The city lies on a glacial terrace formed during the Pleistocene epoch by the recession of the Cordilleran Ice Sheet.