Complex sentence: In 1823 Jedediah Smith and several trappers "rediscovered" the route, and the trail along the Platte, North Platte and Sweetwater Rivers became a major route to the fur traders' summer Rocky Mountain Rendezvous.
Split into simpler sentences: In 1823 Jedediah Smith and several trappers "rediscovered" the route. The trail along the Platte, North Platte and Sweetwater rivers became a major route of fur traders to their summer Rocky Mountain Rendezvous.