The Sewickley Branch started at the Pennsylvania Railroad's Southwest Branch at Youngwood, PA, and served local mines to the east. It was composed of several smaller branches:
- The Sewickley Branch
- The Boyer Run Branch
- The Brinker Run Branch
- The Mammoth Branch
- The Bessemer Branch
- The Margeurite Branch
Each of these branches were named for a creek/river to which they ran adjacent, or for a township near the branch's end.
As the mines dwindled in output, so did the usefulness of the lines, until they were all abandoned by the 1980s.