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. The ridges traditionally contained the westward spread of urbanization, forming a significant geologic barrier beyond the piedmont west of the Hudson River; the town of Newark, for example, once included lands from the Hudson to the base of the mountains. Later treaties moved the boundary to the