Charleston Lake Provincial Park is situated on the Frontenac Arch, a finger-like extension of the rugged Canadian Shield to the north, which connects the Canadian Shield with the Adirondack Mountains of New York State to the south. Steep, rocky slopes line much of Charleston Lake’s shoreline, while the inland terrain is equally rugged with abrupt ridges and valleys. Blue Mountain, situated in the eastern portion of the park, is the highest point in the county, rising 108 metres above the lake and affording spectacular views of the surrounding area.

In addition to the rugged and ancient Precambrian rock of the Canadian Shield, the main peninsula of the park is primarily a younger, flat-lying sandstone plateau, from which unique caverns and rock overhangs were formed. This unique mix of older Precambrian rock and younger sandstone makes Charleston Lake a geologically intriguing and picturesque landscape. In addition to the geologic information included in the introduction about the origins of the bed rocks of the Park, an understanding of the many complex forms of formations would be assisted with some brief comments.

The sandstone of CLPP includes cross bed sequences up to several meters thick, indicating cyclical inundation events, perhaps from tidal action along a margin of an ancient river or sea. Studies suggest the pillars or cylinders such as the large one on the Sandstone Island trail past the "caves", are the fossilized remains of artesian springs that developed in response to upwelling water flow through very clean and well sorted sand overlying the hills and valleys of the Cambrian surface.

All this some 450 to 500 thousand years ago. Sandstone pillars are the metamorphasized interior or molds of the cylinders that have been freed from the encircling stone. There are several other excellent examples in the Park. A poster displayed in the visitor centre museum explains with picture and description these unique geological features.