Basilan is the largest island in the Archipelago. Its northernmost point is about 10 miles directly south of Zamboanga. The island is more or less circular in outline and has a radius approximately 11 miles long. Its area is about 400 square miles. Two prominent headlands projecting, one on the east and one on the west, give the island a maximum length of 36 miles. The greatest width, north and south, is 24 miles. The eastern headland is long and has a picturesque, conical peak, called Mount Matangal, which rises about 648 meters above sea level. This peak is a very prominent landmark, visible to a great distance from all points in the Celebes Sea and in the Straits of Basilan. The western headland is less prominent. It has an isolated peak about 287 meters above the sea, immediately north of the settlement of Pangasa'an. The position of this peak makes it a conspicuous landmark to vessels entering the Straits of Basilan from the Sulu Sea. The surface of the island is high and hilly. Twenty-three peaks are recognized, forming two distinct series or ranges, central and peripheral. The central region of the island is an elevated tableland, out of which rise a number of peaks forming the central series and ranging from 609 to 1,019 meters above sea level. A thick forest covers this region. The rivers are small and dry up in the dry season. Few Yakans are to be found there, and their houses are isolated and far apart. No cultivation is carried on in the interior. On the outside of this region rises the peripheral series of hills or peaks which lies parallel and near to the coast. With the exception of two, all of these peaks are below 304 meters in height. The drop from this line of hills to the coast is rapid in some places, and in general the shore line is low and swampy and covered with mangrove trees. The three largest valleys in the island are those of Gubawan or Lamitan on the northeast, Kumalarang on the northwest, and Malusu on the west. This region is generally considered fertile, but it has a marked dry season and droughts are not rare.