Complex sentence: Lindsay Applegate, accompanied by fourteen other settlers in the Willamette and Rogue valleys in western Oregon, established the South Emigrant Trail in 1846 between a point on the Oregon Trail near Fort Hall, Idaho and the Willamette Valley.
Split into simpler sentences: Lindsay Applegate, accompanied by fourteen other settlers in the Willamette and Rogue valleys in western Oregon, established the South Emigrant Trail in 1846. It connected a point on the Oregon Trail near Fort Hall, Idaho and the Willamette Valley.