The Central Depression is in the center of the state. It is an extensive semi flat area bordered by the Sierra Madre de Chiapas, the Central Highlands and the Northern Mountains. Within the depression there are a number of distinct valleys. The climate here can be very hot and humid in the summer, especially due to the large volume of rain received in July and August. The original vegetation was lowland deciduous forest with some rainforest of middle altitudes and some oaks above above sea level.