El Yunque National Forest, formerly known as the Luquillo National Forest and the Caribbean National Forest, is located on the island of Puerto Rico. It is commonly known as only El Yunque, a Spanish approximation of the aboriginal Taino word "Yu-ke", thought by scholars to mean "White Lands". However the lightning storms that occur there were to the Spaniards the sound of a giant hammer hitting an anvil (yunque in Spanish). It is also the name of the second highest mountain peak in the Forest. El Yunque is the only tropical rain 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 28,000 acres (43.753 mi² or 113.32 km²) of land, making it the largest block of public land on the island of Puerto Rico. El Toro, the highest mountain peak in the forest rises 1,065 metres (3,537 ft) above sea level. In descending order of land area the forest is located in the municipalities of Río Grande, Naguabo, Luquillo, Ceiba, Canóvanas, Las Piedras, Fajardo, and Juncos.[3] Forest headquarters are located in Río Grande.