Much of Devils Tower National Monument is forested. Although several types of trees are found here, the dominant species is ponderosa pine. These pine forests are dotted with juniper, aspen, and bur oak trees. Ponderosas stand like ancient sentinels above them all. The ponderosa pine is found from Mexico to Canada. They can grow to over 100 feet tall and live more than 300 years. Like many conifers, they keep their green needles all year long; from a distance, however, these dark pines appear almost black, giving rise to the name 'Black Hills' (an English translation of the Lakota name 'Paha Sapa').