| Reason Run | |
| Name Other: | Tributary to Youghiogheny River |
| Map Size: | 300 |
| Pushpin Map: | USA Pennsylvania#USA |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of Reason Run mouth |
| Pushpin Map Alt: | Map of Reason Run mouth location |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Pennsylvania Maryland |
| Subdivision Type3: | County |
| Subdivision Name3: | Fayette (PA) Garrett (MD) |
| Length: | 2.19miles[1] |
| Discharge1 Location: | Youghiogheny River in Youghiogheny River Lake |
| Discharge1 Avg: | 2.79cuft/s at mouth with Youghiogheny River[2] |
| Source1: | Buffalo Run divide |
| Source1 Location: | about 1 mile northeast of Asher Glade, Maryland[3] |
| Source1 Coordinates: | 39.7103°N -79.4272°W[4] |
| Source1 Elevation: | 1820feet |
| Mouth: | Youghiogheny River in Youghiogheny River Lake |
| Mouth Location: | about 1.5 miles southwest of Somerfield, Pennsylvania[5] |
| Mouth Coordinates: | 39.7281°N -79.4081°W |
| Mouth Elevation: | 1439feet |
| Progression: | Youghiogheny River → Monongahela River → Ohio River → Mississippi River → Gulf of Mexico |
| River System: | Monongahela River |
| Tributaries Left: | unnamed tributaries |
| Tributaries Right: | unnamed tributaries |
| Bridges: | Guard Road |
Reason Run is a 2.19miles long 1st order tributary to the Youghiogheny River in Fayette County, Pennsylvania.
Reason Run rises about 1 mile northeast of Asher Glade, Maryland in Garrett County,[3] and then flows north-northeasterly into Fayette County, Pennsylvania to join the Youghiogheny River in Youghiogheny River Lake about 1.5 miles southwest of Somerfield.[5]
Reason Run drains of area, receives about 46.7 in/year of precipitation, has a wetness index of 330.63, and is about 75% forested.[2]