Complex sentence: The French expedition of Joliet and Marquette in 1673 found none of the towns or people that the Spanish had documented; all that remained were the many mounds that still dot the landscape along the rivers and creeks.
Split into simpler sentences: The French expedition of Joliet and Marquette in 1673 found none of the towns or people that the Spanish had documented. All that remained were the many mounds that still dot the landscape along the rivers and creeks.