Welcome to my first EarthCache! This time, we will visit very interested rocks near Hudson River. You will need a ship or boat. There are plenty of places around the river where you can rent a boat. If you have your own boat, it's probably best to park at Trailhead and sail here. I hope you will enjoy this adventure!
Geology
The narrow and winding course of the Hudson in this area is fascinating, especially considering the fact that the river is actually an estuary here, having already reached sea level at Newburgh, NY, several miles to the north. The river is significantly wider, and the shorelines more gently sloping, both north and south of the Highlands.
Look around the posted coordinates. The rocks you can see here is very old (about 1.3 to 1.1 billion years - these are the oldest exposed rocks in NY) deformed along with the rocks of the Adirondack Mountains during the Grenville Orogeny.
Grenville Orogeny in the USA
It was very long Mesoproterozoic event, which created mountains at North American continent. Right here it changed the original rocks at enormous temperatures and pressures in transformed rocks.
This interesting geomorphology played a significant role in the outcome of the Revolutionary War, when south of today's Bear Mt. Bridge, colonial forces built a chain floating on large logs across the Hudson to stop the British fleet from advancing into the interior of the territory. Several fortresses were built along the river (the closest from here is the US Military Academy at West Point north of here) and communication was provided by a series of signal smoke on the mountain tops along the river.
Questions:
1. What manifestations of Grenville Orogeny can you see directly from here?
2. How old are these rocks?
3. How has the Grenville Orogeny changed the course of the Hudson River?
4. Take a picture with you or with your GPS near the posted coordinates.
Send me answers via profile. I will contact you if some answers will be wrong. Thank you for visiting!
Sources:
Wikipedia