El Yunque is also what the 28,000 acre National Forest that sprawls across El Yunque-the mountain is called. It is by far the smallest National Forest in the United States (Puerto Rico is considered part of the United States where National Forests are concerned), and the only one that is tropical. Not only is this the smallest forest in the system, but it is the most diverse, with over 150 different species of trees crammed into the small area. It receives over 15 feet of rain each year on average.

Caribbean National Forest (the more formal name) is one of the oldest protected areas in the Western Hemisphere by virtue of having been set aside by the Spanish Crown in 1876 while Puerto Rico was still ruled from Madrid. In reality this proclamation was made to keep enemies from accessing the wood that grows in the forest to make strong ships. On the ground, this translates into virgin forest that looks much as it did when Christopher Columbus visited Puerto Rico 500 years ago.

For the local Taino Indians, the forest was a sacred place. Petroglyphs can be found in some remote parts of these mountains. The forest is named for an Indian spirit Yuquiye, who was believed to live in the high peaks of the nearby mountains.