Streams with healthy forest buffers, unlike what is shown here, help reduce flooding and erosion of valuable soil.

The first known reference to Rock Creek by its current name is shown on a survey draft of the Manor of Mask for the William Penn family in 1766. Following this reference, Rock Creek was referred to as Rock Run. It was named for the large boulders that are still commonly found in the watershed. These boulders, known locally as Gettysburg granite or trap rock, were formed 180 million years ago during the Triassic Period, when the continents were separating from Pangea and the Atlantic Ocean was forming. Motlen rock was forced into the cracks of the existing shale, siltstone, and sandstone. The molten rock cooled to form the boulders we now see in areas like Devel's Den, Culp's Hill, and Big and Little Round Tops.