Valleys in New Jersey were filled with glacial lakes during the last ice age. Sediment evidence shows that gravel deposits in these lakes came from tunnels under the glaciers. These deposits contain gravel from the local area and form linear ridges called eskers. The deposits were likely formed by tunnels under the ice that extended for long distances and lasted for over a thousand years. These deposits are important sources of water and can be found beneath silt and clay layers in the lake bottoms. Understanding how these deposits formed is crucial for finding and managing water resources.