Complex sentence: The Grave Creek Mound was believed probably first discovered by Joseph Tomlinson between 1770, when he and his brother built a log cabin at Grave Creek Flats, and 1772 when he built a cabin from the mound for his family.
Split into simpler sentences: The Grave Creek Mound was believed first seen by a European American when Joseph Tomlinson and his brother built a log cabin at Grave Creek Flats in 1770. Two years later, Joseph built a cabin from the mound for his family.