The Watchung Mountains (once called the Blue Hills) are a group of three long low ridges of volcanic origin, between 400 and 500 feet (120 and 150 m) high, lying parallel to each other in northern New Jersey in the United States. The Watchung Mountains are known for their numerous scenic vistas overlooking New York City, Newark and New Jersey skylines, as well as their isolated ecosystems containing rare plants, endangered wildlife, rich minerals, and globally imperiled trap rock glade communities.