Complex sentence: The turned south from the northern Utah Territory (Nevada) and, when encamped at Nevada's Carson Valley on January 31,1844; guide Kit Carson suggested the expedition detour west during the winter conditions to Sutter's Fort in California for supplies.
Split into simpler sentences: The turned south from the northern Utah Territory (Nevada). When encamped at Nevada's Carson Valley on January 31,1844; guide Kit Carson suggested the expedition detour west during the winter conditions to Sutter's Fort in California for supplies.