Simplify the following text for a Grade 12 native English-speaking person.
Original: The island has five major mountain ranges : The Central Range , known in the Dominican Republic as the Cordillera Central , spans the central part of the island , extending from the south coast of the Dominican Republic into northwestern Haiti , where it is known as the Massif du Nord .
Simplified: The sources of the longest rivers of Hispaniola are found in the mountains of the Cordillera Central ( Dominican Republic ) - Massif du Nord ( Haiti ) .