Geologic image in the Kentucky Geological Survey data repository.Image Name: Earth History, Letcher County Image Date: 10/3/2007 Category: photo_outcrop Source: Carey, Dan Format: JPG Size (MB): 0.7 Pixel Dimensions: 1624 x 1596 Description: From the 355-million-year-old shale in the Mississippian Pennington Formation at the bottom to the 315-million-year-old sandstone in the Lee Formation at the top, nearly 40 million years of the earth's history can be seen in the tilted bands of rocks in Pine Mountain along U.S. 23 at Pound Gap in Letcher County. Photo by Dan Carey, Kentucky Geological Survey.