 The stream is part of the greater 57.7- square-mile Drainage basin, or watershed, located in the north-central portion of Fairfax County and drains directly to the Potomac River.Difficult Run flows through Fairfax County to Great Falls Park, on the Virginia side of the Potomac River.The portion of the run through the park has been characterized as "a miniature Mather Gorge and Great Falls."