There are three distinct regions: the coastal plains (ranging between  from the ocean's shore), the mountains (the Cristal Mountains to the northeast of Libreville, the Chaillu Massif in the centre), and the savanna in the east. The coastal plains form a large section of the World Wildlife Fund's Atlantic Equatorial coastal forests ecoregion and contain patches of Central African mangroves especially on the Muni River estuary on the border with Equatorial Guinea.