What part of the country are you talking about? I’ve never heard a branch called a run.
W.MD/northwestern WV/VA/southwestern-central PA.
All in the Appalachians.
Just within a mile or 2 of me, there’s Lane’s Run, Rattle Run, Rabble Run, Tom’s Run, Hinckle Run, Indian Springs Run and Cherry Run.
And those are just the ones I can think of, off the top of my head.
Just because you never heard of it don’t mean it ain’t so...:)