Natural regions: In the former western state, however, the mass of Mount Cameroon reaches almost to the sea. The plain is densely forested including areas of Central African mangroves especially around Douala and in the estuary of the Cross River on the border with Nigeria. In western Cameroon is an irregular chain of mountains, hills, and plateaus that extend from mountains. It also contains some of the country's most fertile soils, notably around volcanic mountains. This area of tropical forest has been categorize by the World Wildlife Fund as the Cameroonian Highlands forests ecoregion with Mount Cameroon considered separately because as an active volcano it has a distinct environment from the other mountains.