These areas vary in climate, elevation, and landscape, providing dramatic contrasts between hot and humid tropical lowlands and highland peaks and valleys.

The southern edge of the western highlands is marked by the Sierra Madre, which stretches from the Mexican border south and east, and continues at lower elevations toward El Salvador.

The mountain chain is characterized by steep volcanic cones, including Tajumulco Volcano 4,220 m or 13,845 ft, the highest point in the country and Central America.

The rivers are short and shallow in the Pacific vertient, larger and deeper, such as the Polochic which drains in Lake Izabal, Río Dulce, Motagua and Sarstún that forms the boundary with Belize in the Caribbean and the Gulf of Mexico vertient (Usumacinta, which forms the boundary between Chiapas, Mexico and Petén and its tributaries such as La Pasión and San Pedro.

Volcán Tajumulco, 4,220 m, the highest point in Central America, is located in the western department of San Marcos.