Complex sentence: At its peak it included a post office, grocery store, and school house, in addition to residences; the school house is the solitary remaining building, and is currently in use by Breitburn Energy, who operates much of the field.
Split into simpler sentences: At its peak it included a post office, grocery store, and school house, in addition to residences. The school house is the solitary remaining building, and is currently in use by Breitburn Energy, who operates much of the field.