<P> Geologically , the falls were formed at the end of the last ice age approximately 13,000 years ago . Formerly the Passaic had followed a shorter course through the Watchung Mountains near present - day Summit . As the glacier receded , the river 's previous course was blocked by a newly formed moraine . A large lake , called Glacial Lake Passaic , formed behind the Watchungs . As the ice receded , the river found a new circuitous route around the north end of the Watchungs , carving the spectacular falls through the underlying basalt , which was formed approximately 200 million years ago . </P>
<P> Geologically , the falls were formed at the end of the last ice age approximately 13,000 years ago . Formerly the Passaic had followed a shorter course through the Watchung Mountains near present - day Summit . As the glacier receded , the river 's previous course was blocked by a newly formed moraine . A large lake , called Glacial Lake Passaic , formed behind the Watchungs . As the ice receded , the river found a new circuitous route around the north end of the Watchungs , carving the spectacular falls through the underlying basalt , which was formed approximately 200 million years ago . </P>
the great falls of paterson flows over what type of rock
the great falls of paterson flows over what type of rock
basalt
basalt