The Hudson River valley runs in a north-south direction across eastern New York State. There are many rock types in the valley. This includes Triassic sandstones and redbeds in the south, and the Palisades Sill. Older Precambrian gneiss is in the north (and east).
In the Hudson Highlands, the river enters a fjord. This fjord was cut during previous ice ages. To the west are the very long Appalachian highlands. Near Tappan Zee Bridge, the west side of the river has high cliffs. They are about 400–800 feet high.
During the last ice age, the valley was filled by a large glacier. The glacier went down as far as Long Island. Near the end of the last ice age, the Great Lakes drained south down the Hudson River. The drained water is called Lake Iroquois. Lake Ontario is the remnant of that lake.
- Van Diver, B.B. 1985. Roadside Geology of New York. Mountain Press, Missoula. p. 59-63.
- "Physiographic divisions of the conterminous U. S." U.S. Geological Survey. Retrieved 2007-12-06.
- Eyles, N. Ontario Rocks: Three Billion Years of Environmental Change. Fitzhenry & Whiteside, Markham, Ontario. 339 p.