Complex sentence: The Tar Creek Superfund site is the Oklahoma section of three sites that together encompass the Tri-State district, an old lead and zinc mining district with parts of southwest Missouri, southeast Kansas, and northeast Oklahoma.
Split into simpler sentences: The Tar Creek Superfund site is the Oklahoma section of three sites that together encompass the Tri-State district. This is an old lead and zinc mining district that included parts of southwest Missouri, southeast Kansas, and northeast Oklahoma.