Complex sentence: Greensburg, PA is located on a large vein of bituminous coal about 30 miles east of Pittsburgh which needed coal and coke for steel mills that were built in Pittsburgh in the 1870s and 1880s.
Split into simpler sentences: Greensburg, PA was located on a large vein of bituminous coal about 30 miles east of Pittsburgh. Coal and coke were needed for steel mills that were built in Pittsburgh in the 1870s and 1880s.