The state has a complex geography with seven distinct regions according to the Mullerried classification system. These include the Pacific Coast Plains, the Sierra Madre de Chiapas, the Central Depression, the Central Highlands, the Eastern Mountains, the Northern Mountains and the Gulf Coast Plains. The Pacific Coast Plains is a strip of land parallel to the ocean. It is composed mostly of sediment from the mountains that border it on the northern side. It is uniformly flat, and stretches from the Bernal Mountain south to Tonalá. It has deep salty soils due to its proximity to the sea. It has mostly deciduous rainforest although most has been converted to pasture for cattle and fields for crops. It has numerous estuaries with mangroves and other aquatic vegetation.