 These mountains form a link between the Cordillera Central and the Sierra Madre mountain ranges, separating the Cagayan Valley from the Central Luzon plains.The central section of Luzon is characterized by a flat terrain, known as the Central Luzon plain, the largest in the island in terms of land area.The plain, approximately in size, is the country's largest producer of rice, and is irrigated by two major rivers; the Cagayan to the north, and the Pampanga to the south.