"The Mianus River Gorge was formed by the rushing waters of the Wisconsin glacier which began melting 10,000 to
15,000 years ago. The water found a weakness in the
confining rock and formed a cascade. In time, the erosive effect of the
water weakened the face of the waterfall, causing it
to move steadily backward, leaving a long narrow channel. Thousands of years
of rushing water widened and deepened the initial breach, leaving the Gorge as we see it
today."
retrieved from http://www.mianus.org/wp-content/uploads/2011/06/MRGP_map.pdf October 2014