REMARKS: An undisturbed relic of a former periglacial climate, 40 yards by 1140 yards in an area, having a gradient from 1.5 to 4.5 degrees. The field is composed of subangular boulders of Pottsville conglomerate and sandstone (Pennsylvanian age) derived from adjacent ridges of Sharp and Stony Mountains.
REFERENCES: Martin, R. A. [1971], Geology of the Devil's Racecourse Boulderfield, Dauphin County, Pennsylvania, M. S. thesis, Millersville State College, Millersville, Pennsylvania, 27 p.
REMARKS: An exceptional view (north) of the Valley and Ridge province; encompasses Powells Valley, Berry Mountain, Mahantango Mountain, and the meandering Susquehanna River.
REMARKS: The most outstanding site in Pennsylvania from which to view the Susquehanna Water Gap in Blue Mountain and the different erosion levels of the Appalachian Mountains, commonly thought to be peneplain surfaces. The peneplain concept is a major geologic controversy. The Schooley (Cretaceous) Peneplain is believed to be represented by the relatively even-crested tops of the mountains at 1400 to 1600 feet in elevation. The Harrisburg (late Tertiary) Peneplain is developed in the Ordovician shales and limestones, largely the Martinsburg Formation, at about 600 feet. The level near the present floodplain of the Susquehanna River and Conodoguinet Creek (about 320 to 350 feet) has been called the Summerville Peneplain. Some geologists have correlated the Harrisburg Peneplain with the Allegheny Peneplain (1250 feet) of western Pennsylvania and the Summerville with the Worthington (900 feet) of western Pennsylvania.
Reservoir Park is underlain by conglomerates in the Martinsburg Formation. This is an unusual occurence, although sandstones are common.
REFERENCES: Ashley, G. H. (1933), The scenery of Pennsylvania, Pennsylvania Geological Survey, 4th ser., General Geology Report 6, 91 p.
Pittsburgh Geological Society (1955), Field guidebook of Appalachian geology, Pittsburgh to New York, American Association of Petroleum Geologists, Annual Meeting, New York, New York, March 28-31, p. 45.
REMARKS: The area of five water gaps along the Susquehanna River north of Harrisburg was designated as a registered National Natural Landmark. The geologic record of hundreds of millions of years is recorded in the rocks exposed in the five gaps, visible at a number of points on both sides of the river.
REFERENCES: Ashley, G. H. [1931], A syllabus of Pennsylvania geology and mineral resources, Pennsylvania Geological Survey, 4th ser., General Geology Report 1, p. 79-80.
Pennsylvania Geology (1969), Susquehanna Water Gaps dedicated, v. 1, no. 2, p. 4-5.