It's probably an old Iron Ore mine.
You can visit the ones at Pigeon Mountain at the Estelle Mine Trail (near the pocket). The mines there were dug around the turn of the century. They look very similar to the one in the video above. Iron Ores are rocks and minerals from which metallic iron is extracted in which they use to make steel. At the height of the Estelle Mines it employed 235 men. This mining community provided over 175 homes for the miners and their families. A commissary was also provided for all the needs of the employees and their families. There were two schools with an enrollment of 190 children. The Estelle property consisted of 1600 acres and had a blacksmith shop, machine shop, and carpenter shop, steam plant, sawmill and a supply house. There was a 6-mile narrow gauge railroad called the "Dinky" which began at the crusher and ran through 7 tunnels to the mines. Ore was hauled from the mines to the crusher on this railroad. As the demand for ore started to wane, operations at the mines began to slacken and finally ceased in 1924. At the height of its operation and due to a shortage of qualified miners, boys as young as seven would help load ore. Ten-year-old boys worked at the crusher and at the age of 12, the boys could go underground as "mule" boys. The mule boys worked 10 hours a day for 20 cents per hour. Push boys, crushers, firemen, engineers and breakies were some of the other jobs available to the men and boys who lived in the area. Sunday was the day off and was the day for recreation. I suspect that many of them even found enjoyment in the nearby falls at the "Pocket". The town is now gone and nothing is left except the mines and some tombstones in the nearby cemetery. It is essentially a ghost town.
Here is a video I put together a few years ago about those:
http://www.youtube.com/watch?v=UBk2AKG7sJk