Watkins Run (Calvin Run tributary)Watkins Run is a long first-order tributary to Calvin Run in Greene County.CourseWatkins Run rises about 2.25 miles north of Mount Morris, Pennsylvania, and then flows southerly to join Calvin Run about 0.25 miles north of Mount Morris, Pennsylvania.WatershedWatkins Run drains of area, receives about 43.2 in/year of precipitation, and is about 85.3% forested.