Complex sentence: The region was visited by the explorers Robert de La Salle and René de Bréhant de Galinée in 1669 during which time they observed a burning spring known to the Seneca in the nearby Town of Bristol.
Split into simpler sentences: The region was visited by French explorers Robert de La Salle and René de Bréhant de Galinée in 1669. They recorded seeing a burning spring known to the Seneca in what is now known as the nearby Town of Bristol.