 Geologically, Sourland Mountain is composed of sedimentary and igneous rocks of Late Triassic and Early Jurassic age, and are part of the Newark basin rift lake system.The main ridge in Sourland Mountain is intrusive diabase (a type of igneous rock) associated with the same igneous event that produced the Palisades Sill (the cliffs along the west side of the Hudson River across from New York City), and The Watchung Mountains in Northern New Jersey.The sedimentary rocks are Late Triassic in age and are part of the lower Passaic Formation of the Newark Basin sedimentary sequence.