Northeast of the city, located in the Sierra Norte or Sierra Juarez, are the three districts of Ixtlan, Mixe and Villa Alta. Their combined surface area is 9348 km2 (3609 miles2) which covers approximately 10% of the state. This is the land of the Cuinantecas, the Zapotecs and the Mixes. Here you find mountains of up to 3500m high (11500 feet), pine forests, meadows and rivers. The region is set in a unique location; seven of the nine types of vegetation existing in Mexico can be found here, boasting nearly four thousand plant species. This means that in the space of a few hours, it is possible to see ecosystems that in other parts of the world are separated by thousands of miles. The mixed pine-oak forests have been classified by the World Wildlife Fund as one of the most varied on earth and one of the oldest ecosystems in the world, estimated to be over twenty million years old.