Watchung Outliers

The Watchung Outliers include six areas of isolated low hills and rock outcrops of volcanic and sedimentary origin in the U.S. states of New York, New Jersey, and Pennsylvania.

These geologic outliers are primarily diminutive and detached remnants of the Triassic/Jurassic age Watchung Mountain basalt flows with intervening layers of sedimentary rock.

All six of the outliers are found along the western edge of the Newark Basin, occupying small synclines adjacent to the Ramapo fault system.

New research indicates that the vicinity of Ladentown may have served as the primary vent from which the magma of the Palisades Sill erupted to the surface to form the Watchung flood basalts.

Finally, lying within and above the band of sedimentary rock is a central area of Preakness Mountain Basalt which constitutes the portion of the outlier reduced by quarrying.

[3] Dikes branching south from the vicinity of the outlier appear to be connected to the intrusive igneous Sourland Mountain, an extension of the Palisades Sill.

[9][10] In this respect, Prospect Hill likely marks another location where the Palisades magma found a way to the surface, albeit not as significant as in the Ladentown Outlier.

A low ridge composed of Orange Mountain Basalt forms a horseshoe around the eastern edge of a belt of sedimentary strata from the Feltville Formation.

The diabase, which lies stratagraphically below the basalt, is thought to have been intruded into the syncline containing the Jacksonwald Outlier during or after some degree of folding had affected local strata.