Glacial deposits of debris 20 to 30 feet ( 6.1 to 9.1 m ) thick formed a dam blocking water from Ganoga Lake .
What became Lake Jean from draining into Big Run , a tributary of Fishing Creek .
Glacial deposits of debris 20 to 30 feet ( 6.1 to 9.1 m ) thick formed a dam blocking water from Ganoga Lake and what became Lake Jean from draining into Big Run , a tributary of Fishing Creek .