Complex sentence: It once had the tallest mound in Louisiana at in height and the second-tallest mound in North America (after Monk's Mound at Cahokia Mounds), but it was destroyed to make way for the Jonesville bridge over the Black River.
Split into simpler sentences: It once had the tallest mound in Louisiana at in height; it was the second-tallest mound in North America (after Monk's Mound at Cahokia Mounds). This mound was destroyed to make way for the Jonesville bridge over the Black River.