Puerto Rico, 3,700 mi2 (9,600 km2)
Land-surface form.--Puerto Rico occupies a tropical oceanic position just south of the Tropic of Cancer (lat. 23 1/2N.). It is one of easternmost peaks of a partly submerged mountain range composed of folded Cretaceous and older rocks that have been cut by granitic intrusions. East-west trending ridges and peaks form the backbone of the island. Local relief is considerable, and slopes are steep. The highest peak in the Cordillera Central has an altitude of 4,389 ft (1,338 m). This terrain is flanked by marine limestone forming low plateaus with a karsts topography.
Climate.--Puerto Rico has a tropical climate. The surrounding oceans and the persistent northeast trade winds maintain almost uniform climatic conditions throughout the year. But there is seasonality in precipitation, with a maximum occurring during the high-sun period, and precipitation varies greatly with altitude and exposure.
San Juan, on the north coast, has average temperatures ranging from about 75F (24C) in January to about 80F (27C) in July. Temperatures on the south coast average roughly 1F higher. For every rise in elevation of 1,000 ft (300 m), temperatures fall about 3 1/2F (2.2C). Frost is rare below 4,000 ft (1,200 m) and has never been recorded below 2,500 ft (800 m).
Precipitation is heaviest on the windward sides of the island; lee slopes are semiarid. The trade winds, blowing from just slightly north of east, first reach the Sierra de Luquillo, which has an average annual rainfall of more than 200 in (510 cm). Leeward of the Sierra de Luquillo is rain shadow. Rainfall is considerable in the Cordillera Central, especially in the west. Annual rainfall on the north coast, at San Juan, averages 61 in (1,560 mm); leeward of the Cordillera, rainfall is much less, averaging 35 in (890 mm) per year on the south coast, at Ponce. The island is in the hurricane belt. Hurricanes winds may exceed 100 mi/h (161 km/h) and be accompanied by torrential rain.
Vegetation.--Most of Puerto Rico is under cultivation, but some rainforest remains on the wet north slopes of mountains such as the Sierra de Luquillo. Forest trees include mahogany, ebony, mamey, tree ferns, sierra palm, mango, Spanish cedar, sandalwood, and rosewood. They are associated with orchids, jungle vines, and matojo grass. Semiarid southern slopes support a dry forest association of acacia, royal palm, yucca, cacti, and dry grasses. Mangrove grows in swamps along much of the coast.
Soils.--Much of the island is covered by thick residual soil containing about equal amounts of Oxisols, Ultisols, and Inceptisols.
Fauna.--Puerto Rico has never had any large wild mammals. Native bats and lizards, along with the intentionally introduced mongoose and the unintentionally introduced rat, probably constitute nine-tenths of the island's vertrebrates vertebrates. The Agouti and armadillo are practically extinct.
The endangered Puerto Rican parrot occurs only here.
The boa, giant turtle, and several lizards are practically extinct. The coqui is a distinctive frog.
Offshore there is considerable coral and sport fishes abound in the coastal waters.