Rock Cities are massive outcrops of conglomerate beds found at higher elevations throughout the region. They were formed at the edge of an inland sea from sediments eroded from the ancient Taconic mountains to the east. The conglomerate basically consists of white quartz pebbles of various sizes embedded in sandstone. Pebbles from different time periods indicate the conditions under which they were deposited. For example, the Pennsylvanian (~325-280 million years ago) Olean conglomerate at Rock City Park contains well rounded pebbles deposited in a turbulent marine environment such as a shallow estuary. Devonian (~395-345 million years ago) beds like those at Thunder Rocks and Little Rock City contain flattened pebbles, suggesting deposition in a deeper, less turbulent environment. Conglomerate beds around Olean, NY are the only Pennsylvanian and Mississippian (together known as the Carboniferous period) deposits in New York State. As the beds crop out of the hillsides, water seeps into fissures, freezing and thawing to produce huge blocks. The water also erodes shale beds beneath them, causing them to break apart and slowly slide downslope with soil creep. This results in rock cities, with narrow street-like passageways and tunnels. There are numerous rock cities, located in Warren, McKean and Potter counties in Pennsylvania as well as Cattaraugus and Allegany counties in New York. There is even one in Chautauqua County. Three well known rock cities from Cattaraugus County are represented below.
Rock City Park
I tried to avoid the "postcard" views, but I couldn't escape this one from atop the rocks at Rock City Park. That the region is a dissected plateau is evident from the relatively level horizon.
Rock City Park
Located south of Olean, NY, Rock City Park is the largest and most famous of the area's rock cities.
Rock City Park
What appear to be saplings growing out of the rocks here are actually older trees with stunted growth. Some of the trees are 50 to 100 years old.
Rock City Park
Since the early 1900's, when an electric trolley line brought visitors from Olean, NY and Bradford, PA, Rock City Park has been a favorite picnic and hiking place.
Roadside Rocks
Many of the conglomerate outcrops are remnant or limited. Small formations like this one along SR 16 between Olean and Rock City, NY are frequently seen.
Thunder Rocks
Thunder Rocks is one of two larger rock cities (several smaller ones exist) in Allegany State Park. This rock city is more disjointed than others, because rather than outcropping, it forms a remnant cap at the top of a hill.
Little Rock City
Near Little Valley, NY, Little Rock City is a quiet little public space for a relaxing hike.
Little Rock City
The fissures at Little Rock City are impressive, though not as deep as those at Rock City Park.
Little Rock City
There are plenty of nooks and crannies to explore at any rock city.
Located south of Olean, NY, Rock City Park is the largest and most famous of the area's rock cities. 
What appear to be saplings growing out of the rocks here are actually older trees with stunted growth. Some of the trees are 50 to 100 years old.
Since the early 1900's, when an electric trolley line brought visitors from Olean, NY and Bradford, PA, Rock City Park has been a favorite picnic and hiking place. 
Many of the conglomerate outcrops are remnant or limited. Small formations like this one along SR 16 between Olean and Rock City, NY are frequently seen.
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