City Of Rocks National Reserve - Geology

City of Rocks was designated a national natural landmark in recognition of the nationally significant geological and scenic values of its rock formations. Rock formations in the reserve developed through an erosion process called exfoliation, during which thin rock plates and scales sloughed off along joints in the rocks. The joints, or fractures, probably resulted from contractions when the rock cooled or from expansions when overlying materials eroded away and eliminated confining pressure. The granite has eroded into a fascinating assortment of shapes as high as 200 feet. There are more than 500 panholes in one small area in the reserve. The most notable panhole is located on top of Bath Rock and frequently fills with water from rain or snow melt.