Mount Arayat is 2880 feet in height, and in fine weather is plainly visible from Manila and Cavite, and even from the mouth of the bay. The principal rivers of this valley are the Agno, the Dagupan, the Rio Grande and the Rio Chico of Pampanga. The Agno rises in the mountains of Lepanto, runs south through the province of Benguet, and S.W., W. and N.W. in Pangasinan into a labyrinth of creeks communicating by many mouths with the Bay of Lingayen. The river between Dagupan and San Isidro is navigable for vessels drawing seven or eight feet, and such craft could reach Salasa. From there to Rosales only lighters of very small draught could pass, and after a long spell of dry weather rice-boats drawing only one foot sometimes run aground. Its principal tributaries are the Tarlac and the Camiling, with dozens of smaller streams bringing the whole drainage of the eastern slopes of the Zambales mountains from Mount Iba to San Isidro. The Dagupan river rises in the mountains about the limits of Union and Benguet and runs parallel to the Agno to 16° N. lat., and between it and the sea. Then it turns to the westward, and runs past the towns of Urdaneta, Sta, Barbara, and Calasiao, entering the Bay of Lingayen at Dagupan. It has a multitude of small tributaries which are very differently shown on D'Almonte's and Olleros' maps, and undoubtedly this part has never been surveyed. The Pampanga river has its source on the southern slopes of the Caraballo, in about 16° 10' N. lat. It runs south in two branches, the Rio Grande and the Rio Chico; the first, being the easternmost, receives the drainage from the western slopes of the Cordillera del Este, whilst the Chico receives tributaries from both sides in the flat country and also the overflow from the Lake of Canarem.