Complex sentence: The land in the valley is relatively plain, despite of being surrounded by several mountains of volcanos, the latter part of the Central Range, and the region houses almost three quartes of Costa Ricans, including the capital and most populous city, San José.
Split into simpler sentences: The land in the valley is a relative plain, despite being surrounded by several mountains and volcanos, the latter part of the Central Range. The region houses almost three quarters of Costa Ricans, and includes the capital and most populous city, San José.