PGK Art: Boulder Field Natural Area in Hickory Run State Park. The Boulder Field is an unusual formation of glacial origin, striking due to its flatness and relatively large size. The field is approximately 400 by 1,800 feet and is at least 12 feet deep, making it the largest formation of its kind in the Appalachian Mountains. This feature was formed not from the debris of a retreating glacier, but as a result of glacier-related climatic extremes on rock outcrops. Over time, repeated freezing and thawing caused the splitting apart of these outcrops and the gradual movement of the resulting boulders downslope to their present location. The formation, as it appears today, has remained essentially unchanged for the past 20,000 years.