| Big Run | |
| Image Alt: | A photograph of a riverbed amidst a dense forest. The contrasts are stark. The riverbead is large, flat black rocks. The riverbank is distinct for being lined with a very green moss. The forest floor is brown with fallen pine needles. |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | West Virginia |
| Subdivision Type3: | County |
| Subdivision Name3: | Pendleton |
| Length: | 13miles |
| Mouth: | North Fork South Branch Potomac River |
| Mouth Location: | Cherry Grove, West Virginia |
| Custom Label: | GNIS feature ID |
| Custom Data: | 1550331[1] |
Big Run is a river of 13 miles in length, located one-and-a-half miles west of Spruce Knob in Monongahela National Forest, in Pendleton County, West Virginia. It is a tributary of the North Fork South Branch Potomac River.
The river begins as a series of gullies through an open marshland just south of the northernmost bend in Forest Road 112. Between river mile (RM) 12.8 and 12.4, a series of beaver dams causes the valley to transition from wetland into a string of lakes. From the last beaver dam at RM 12.4, a recognizable river emerges. The open field ends and the river enters a forested ravine.
Big Run joins with tributaries Elk Run at RM 5, Teeter Camp Run at RM 3.6 and Sawmill Branch Run at RM 3.2.
The river empties into the North Fork South Branch Potomac River just outside of Cherry Grove, along Snowy Mountain Road just across the bridge over the Potomac.
This is one of a number of Potomac tributaries known as Big Run, including Big Run at Romney and Big Run at Harper.
Big Run Trail (Forest Trail 527) runs along the east bank of upper length of Big Run. A portion of the trail is the remnant of the rail line that served Parsons Pulp and Lumber Company at Horton near Gandy Creek. The trail can be accessed from either Gatewood Trail off of Sawmill Run Road / Forest Road 28/10 at RM 10.9 or the parking lot at the northernmost oxbow of Forest Road 112 .