Complex sentence: Settlements in Utah south of the Wasatch Front stretched from St. George in the southwest to Nephi in the northeast and including the Sevier River valley, the corridor is roughly congruent with the area between present-day Interstate 15 and U.S. Route 89.
Split into simpler sentences: Settlements in Utah, south of the Wasatch Front, stretched from St. George in the southwest to Nephi in the northeast, including the Sevier River valley. The corridor is roughly congruent with the area between present-day Interstate 15 and U.S. Route 89.