Complex sentence: He opened various lines linking Salt Lake City to mining operations, but the ventures lost a substantial amount of money, and during this period also built The Lagoon, a large amusement park in Farmington, Utah.
Split into simpler sentences: He opened various lines linking Salt Lake City to mining operations, but the ventures lost a substantial amount of money. He also built The Lagoon, a large amusement park in Farmington, Utah.