sentences:  There are four main alluvial river valleys in the watershed.The San Juan Creek valley occupies the south portion of the watershed; the heavily urbanized lower (southwest) portion is located in the cities of San Juan Capistrano and Dana Point, while the largely rural (northeast) portion extends well into the foothills of the Santa Ana Mountains.The Arroyo Trabuco valley forms a large alluvial plain called "Plano Trabuco" in the north part of the watershed (part of suburban Rancho Santa Margarita).