Straddling the boarder between Hamden and New Haven, East Rock Park offers visitors an exciting look at one of the most enduring chapters of Connecticut's geological past. The cliff face that is so prominently visible from the southwest shows the eroded remains of a large sheet of magma that solidified underground 200 million years ago. This sheet of magma welled up from the depths of Earth's crust during the breakup of the supercontinent of Pangea. This was the same geologic event that was responsible for the emplacement of Sleeping Giant and West Rock intrusions, and for the formation of the Hartford basin as a whole.
Since having been exposed by millions of years of erosion, the landscape became further altered by the geologically powerful effects of moving ice during the last widespread glaciation which peaked around 20 thousand years ago. The effects of this event on the land can be seen by visitors in and around East Rock Park.
The following interpretive sign, currently on display at the summit of East Rock, illustrates how the moving ice was able to create both erosive, and depositional features.
