This area covers most of the island of Puerto Rico. It includes the interior mountains, hills, mountain sides, and low areas within the mountains. These mountain ranges are La Cordillera Central, La Sierra de Cayey, La Sierra de Luquillo, and La Sierra Bermeja. 35 km from the northern coast and 15 to 25 km from the south coast. Its highest peaks are located between Villalba and Adjuntas.
Much more rain falls on the northern side of the mountain range as compared to the southern side.
The northern side is much steeper than the southern side. La Sierra de Cayey is an extension of La Cordillera Central. It extends from Cayey to Humacao. To the far east its elevation reaches a mere 400 ft. Two ramifications called Sierra Guardarraya and Cuchillas de Panduras extend southeast between Yabucoa and Maunabo.