The Sierra Madre de Chiapas runs parallel to the Pacific coastline of the state, northwest to southeast as a continuation of the Sierra Madre del Sur. This area has the highest altitudes in Chiapas including the Tacaná Volcano, which rises above sea level. Most of these mountains are volcanic in origin although the nucleus is metamorphic rock. It has a wide range of climates but little arable land. It is mostly covered in middle altitude rainforest, high altitude rainforest, and forests of oaks and pines. The mountains partially block rain clouds from the Pacific, a process known as Orographic lift, which creates a particularly rich coastal region called the Soconusco. The main commercial center of the sierra is the town of Motozintla, also near the Guatemalan border.