The southern terminus of I-605 is at the San Diego (I-405) and Garden Grove (State Route 22) Freeways in Seal Beach. From there, it runs roughly north through the Gateway Cities of the Los Angeles Basin. It then shifts north-northeast, crossing the Whittier Narrows and across the San Gabriel Valley. I-605 then ends at its junction with the Foothill Freeway, (I-210) in Duarte, a small city located at the foothills of the San Gabriel Mountains.