New Jersey was once home to a fiery volcano roughly the size of Mount St. Helens – that sits in the same county as a newly mapped fault line.

Rutan Hill, in Wantage, NJ, appears to be and is merely one of many non-descript earthen formations that comprise the topological face of the Garden State.

But that small Sussex county hillock was, 430 million years ago, the Beemerville Volcano – spanning 10 to 20 miles across and spewing with lava and ash for millions of years, according to geologists.

The Beemerville Volcano is considered to be an extinct volcano and all that remains is Rutan Hill and the “volcanic neck.” 

The “neck” – also called the “plug” – is the solidified remains of a volcano’s conduit and plumbing system and is the last impression an extinct volcano leaves.

Geologists say that there is no chance that the volcano can ever erupt – at least not for millions of more years.

But New Jersey was shaken by a new report this week that announced a previously unmapped fault line that also runs through Sussex County.

The study from Columbia University’s Lamont-Doherty Earth Observatory identified the fault line on April 5th – the day a magnitude 4.8 earthquake rocked New York City.

That once in a hundred year shake revealed the structure of the fault line, which experts say could be dangerous for the Big Apple.

The fault line runs south to north and dips into the Earth at a 45-degree angle – meaning the reverberations are sent downward instead of toward the surface.

“Near the epicenter, there was much less damage or shaking than expected from a magnitude 4.8 earthquake, and that was one thing which was peculiar with that earthquake,” author of the study and Columbia professor Won-Young Kim told Gothamist.

Notably, there was not much shaking at the epicenter of the quake in Tewskbury – but it was experienced as a magnitude 4 in New York City, according to the study.

The April quake caused minor damage to 150 buildings in New York City and caused a Brooklyn school to close its gym for repairs.