The Shawangunk Mountains are a northeastern continuation of the same mountain ridge known as the Blue Mountains in Pennsylvania and the Kittatinny Mountains in New Jersey.
To the east of the Shawangunk Mountains is the Wallkill Valley of the north-flowing Wallkill River (which joins with Rondout Creek and then heads into the Hudson River near Kingston). The Wallkill Valley is about 65 miles long and 20 miles wide.
To the west of the Shawangunk Mountains is the Port Jervis trough which stretches for 100 miles along the eastern side of the Allegheny Plateau from Stroudsburg, Pennsylvania, to Kingston, New York. Here is Rondout Creek that flows northeastward and is joined with the Wallkill River heading into the Hudson River.
The Shawangunk Mountains are composed of Shawangunk conglomerate, made of Silurian and early Devonian sediments of white, quartz-pebble, reworked by the wave action along the shores of a sea on the west side of the mountain and formed into hard rock. The Shawangunk conglomerate in turn lies over Ordovician bedrock The Silurian rockers were uplifted in the late Acadian uplift (375-335 million years ago).
At Ellenville, New York the Shawangunks rise 1900 feet above the base of the Port Jervis Trough. The Ice Caves at Sam's Point Preserve are more like a "rock city" where the mountain breaks into huge blocks that tumble down the mountain slope and settle against each other. Winter ice stays in the "cave" openings long into spring and summer.
The ridge was once cast in bluish hues from the many spruce trees there. By the late 1800s, the trees were largely gone and so was the bluish hue.
Minnewaska State Park has two big lakes, Minnewaska and Awosting, along with Mud Pond (a.k.a., Haseco Lake).
At Mohonk Lake Preserve, Skytop, a massive stone fire tower, overlooks the area a thousand feet above the Wallkill Valley.
Lakes Minnewaska, Awosting and Mohonk, lie along fault zones. Their broken rocks were scooped up by Ice Age glaciers.
Source: Van Diver, Bradford B. Roadside Geology of New York. Missoula, Montana: Mountain Press Publishing Company.