Long Island is a wonder of geology and natural resources and should be treated as such. From the south shore plains to the hills of the north, it contains a unique diversity of natural features created over the thousands of years of glacial activity.  Pre-glacial geologic events in the Long Island include the formation of the over 400 million year old metamorphic bedrock that forms the foundation upon which Long Island rests, and the deposition of sand and clay on this bedrock 70 million years ago during the late Cretaceous period.

The two most recent glacial events that most greatly affected the land surface of Long Island was the advance of a massive continental glacier into this region during the Wisconsin stage of the Pleistocene Epoch. The Ronkonkoma and the later Harbor Hill are two sub-stages, or positions, of this ice sheet which occurred on Long Island. The accumulation of rock debris formed two prominent ridges called terminal moraines, leaving the rocky North Shore beaches we know today. As the glaciers receded, the flow of the sediments created the outwash plains of the south shore, barrier islands and the Hempstead Plains supporting one of the few natural praries to exist east of the Appalachian Mountains. 

A few perennial streams drain the county. Most of the longer streams run from the north to the estuaries in the south. A few of them are Valley Stream, Mill River, East Meadow Brook, Bellmore Creek and Massapequa Creek. The north shore drainage is mostly intermittent. Two of the longest creeks are the Glen Cove Creek and Mill Neck Creek. Much of the runoff between Route 25 and 25a enters the ground water through land locked ponds and natural depressions.