The Cordillera reaches up to the tip of Luzon in the north then submerged itself in Pasaleng Bay. It merges with the Caraballo Mountains in the south to connect with Sierra Madre, the longest mountain range in the country. Cordillera and Sierra Madre run parallel to each other northward and are separated only by a wide valley. Cordillera's east side is bordered by patches of rolling plains extending to the South China Sea.
The Cordillera terrain is prominent in the left side of the map, Sierra Madre is a narrow strip in the right side.
Cordillera is the largest and the highest mountain range in the Philippines. It spans a total land area of more than 18,000 km² comprising almost 1/6th of Luzon mainland. The Cordillera People's Alliance estimated that it is around 230 km long, 120 km in its widest span and many of it's peaks are more than 2,000 meters high. (http://www.cpaphils.org/cordillera.htm)
Politically, the north, east and south side of Cordillera is bounded by the four provinces of Ilocos Region - Ilocos Norte, Ilocos Sur, La Union and Pangasinan. Some of the lower mountains in the northern and eastern part of the range are even occupied by the the Ilocos Provinces and La Union. In the west side of Cordillera, the plains belongs to Cagayan and Isabela and the mountainous part (including the Caraballo Mountains) is of Nueva Vizcaya, all of which are provinces of the Cagayan Valley Region.