 Although the rock formations exposed in Leonard Harrison State Park and the Pine Creek Gorge are at least 300 million years old , the gorge itself formed only about 20 @,@ 000 years ago , in the last ice age . Pine Creek had flowed northeasterly until then , but was dammed by rocks , soil , ice , and other debris deposited by the receding Laurentide Continental Glacier . The dammed creek formed a lake near the present village of Ansonia , and the lake 's glacial meltwater overflowed the debris dam , which caused a reversal of the flow of Pine Creek . The creek flooded to the south and quickly carved a deep channel on its way to the West Branch Susquehanna River . 
