Physiographically the island of Guam is divided into two sections, a northern plateau and a higher southern mountain area. The northern plateau is coral-capped and 200 to 600 feet in elevation, with three low volcanic hills, all of which are under 900 feet in altitude. The plateau surface slopes southwestward toward the lowland area drained by the Agana River, and, because of the porous limestone bedrock, this section is crossed by no permanent streams since the few brooks soon disappear in the coralline soil. Soils over the plateau are of relative fertility, but thin and with numerous madreporic outcrops. Forest and scrub cover the area, broken only by a few farm clearings and the cuttings made for roads. The seaward edges of the plateau drop directly to the water on the northeast, and to narrow discontinuous plains separated by rocky headlands on the north and west. On the south an area of low hills marks the descent to the Agana River valley.
An area of volcanic hills lying across the central portion of the island sharply separates the southern region from the northern plateau, and continues southward as a line of peaks along the western coast. The highest, Lamlam Mountain, rises to 1334 feet. On the western side the range descends to a narrow broken coastal plain; on the east it drops through a 500- to 300-foot plateau, and falls to the sea in cliffs and steep slopes. Five east-flowing streams cross the plateau, and with their tributaries have cut the area into valleys and uplands. Erosion has been extreme, and the limestone that once covered the slopes of the peaks has worn away. Vegetation cover over the volcanic area is chiefly sword grass and unsuitable for forage. Forest occurs between Mt. Alifan and Mt. Lamlam, and extends eastward across the island connecting with a belt along the east coast. Numerous small bays indent the southern portion of the island, and the adjacent river valleys and plains are sites of small agricultural villages.
On the west side of the island Apra Harbor, enclosed between Orote Peninsula and Cabras Island, has been greatly improved since the war, and serves as a naval base. Piti, the port of entry, is located at the north end of the harbor area. About five miles northeastward along the coast is Agana, the capital, situated on a low sandy plain at the mouth of the Agana River. Three major demographic changes have occurred since American occupation in 1898: a growth of Guamanian population, an increase in the number of non-residents, and a change in the distribution of native population.