"The Caribbean National Forest or El Yunque Rainforest, is located on the island of Puerto Rico. It is commonly known as only El Yunque (named after the Taíno Indian spirit Yuquiyú, and meaning "Forest of Clouds") which is the main mountain peak in the forest. It is the only tropical forest in the United States National Forest System.

The forest is located on the slopes of the Sierra de Luquillo Mountains in Puerto Rico, and encompasses over 28,000 acres (113 km²) of land; making it the largest block of public land on the Island of Puerto Rico. The highest portion of the mountain rises 1074 meters (3494 ft) above sea level.

The forest covers lands of the municipalities of Canovanas, Las Piedras, Luquillo, Fajardo, Ceiba, Naguabo, and Rio Grande.

The forest region was set aside in 1876 by the Spanish Crown, and represents one of the oldest reserves in the Western Hemisphere. It is home to over 240 species of trees and plants, 26 of which are found nowhere else.

Typical yearly rainfall can be up to 240 inches (6 m) per year. More than 100 billion US gallons (380,000,000 m³) of rainwater fall on the forest per year.

El Yunque is composed of four different forest ecosystems:

Tabonuco Forest
Palo Colorado Forest
Palma Sierra Forest
Dwarf Forest

El Yunque is also reknown for its unique petroglyphs of historical forest tribes."

from Wikipedia (http://en.wikipedia.org/wiki/Main_Page)

more info from the USDA Forest Service:
http://www.fs.fed.us/r8/caribbean/