Complex sentence: Skirting the Little Belt Mountains by driving southeast, he crossed Arrow Creek, passed south through the Judith Gap (the Big Snowy Mountains to the east, the Little Belts to the west), and crossed several tributaries of the Judith River.
Split into simpler sentences: Skirting the Little Belt Mountains by driving southeast, he crossed Arrow Creek. He passed south through the Judith Gap (the Big Snowy Mountains to the east, the Little Belts to the west), and crossed several tributaries of the Judith River.