Rock Creek Assessment

The Watershed
The Rock Creek Watershed is located in south-central Adams County. It encompasses approximately 63 square miles with many tributaries feeding Rock Creek. Rock Creek originates amid farmland and travels south through portions of Gettysburg borough. The waters flow through farms, residential developments and urban landscapes. Rock Creek joins Marsh Creek near the Pennsylvania/Maryland border where they combine to form the Monocacy River. The Monocacy enters the Potomac River which eventually empties into the Chesapeake Bay. 

The highest point of the watershed is at 755 feet elevation at Big Round Top. The lowest elevation is at the confluence of Rock and Marsh creeks at 363 feet. The watershed is characterized by gently rolling topography of low to moderate relief with broad shallow valleys and low ridges through the red shales and sandstones of the Gettysburg and New Oxford formations. Penn-Klinesville-Croton and Penn-Abbottstown-Readington soil mapping units are generally found here. The Diabase occurs as dikes and sills typically forming the narrow ridges, and larger hills of the watershed. The Lehigh-Neshaminy soil mapping units are common to the hills and ridges of the watershed.

The climate is warm summer subtype of a humid continental climate noted for its variable weather patterns related to cyclonic storms and its large temperature range. The average summer temperature is 73 degrees Fahrenheit and the average winter temperature is 23 degrees Fahrenheit. Adams County’s precipitation average is 42.4 inches a year of which about half (22 inches) falls within the growing season of April to September (Adams County Soil Survey). Rock Creek is classified as a warm-water fishery by the Pennsylvania Department of Environmental Protection throughout the watershed.

Rock Creek covers all or portions of 7 different municipalities, including the townships of Straban, Mt. Joy, Cumberland, Mt. Pleasant, and Butler. All of the town of Bonneauville and a portion of Gettysburg are included in the watershed as well as parts of the Gettysburg National Military Park. 

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