Río de la Plata (Puerto Rico) in the context of "Toa Baja, Puerto Rico"

The Northern Karst Belt (Spanish: Cinturón del Carso Norteño) is a limestone karst landscape located in the northwestern region of Puerto Rico. A karst is a topographical zone formed by the dissolution of soluble porous rocks, such as limestone, with features such as mogotes, canyons, caves, sinkholes, streams and rivers, all of which are common on this region of the island. Some of the island's main rivers, including its longest (La Plata River), traverse the karst and form some of the most distinctive Puerto Rican geographical features such as the Camuy caverns. Many of these rivers feed into and are important in the formation of many marshy areas such as the Caño Tiburones wetlands.

The Sierra de Cayey (English: "Cayey Mountains") is one of three subranges of the Cordillera Central mountain range in the main island of Puerto Rico. It is demarcated from the eponymous main subrange of Cordillera Central by the San Cristóbal Canyon on the town boundary between the municipalities of Barranquitas and Aibonito. From west to east, it is concentrated in the municipalities of Aibonito, Cayey, Guayama, and Patillas in the southeastern region of the island. The summit of the mountain range is Cerro La Santa at 2,962 ft. (903 m) and its most recognizable peak is Cerro Las Tetas at 2,759 ft. (840 m). Along with the Sierra de Luquillo in northeastern Puerto Rico, the Cayey mountain range is the smaller subrange of the Cordillera Central.

The Rio Grande de Loíza, which is one of the largest rivers in Puerto Rico, has its sources in this range within the municipality of San Lorenzo. The La Plata River flows through the Cayey Valley where the town of Cayey is located on the northern slope of the range. There are tobacco and coffee crops in the area.