Which cities were major starting and ending points for wagon trains traveling westward? What pattern in location can you find? How would these...

The Oregon and California Trails started from Independence and St. Joseph, Missouri.  Council Bluffs, Iowa was a later jumping off point.  For the Mormon Trail that was going to Salt Lake City, Utah, Nauvoo, Illinois was the primary location.  All of these places were quite close to rivers and were growing western towns.  The towns themselves grew between the period of 1840 and 1860 due to American westward migration and to the towns and merchants moving there wanting to sell the "greenhorns" things.  All of these places were close enough to be reachable by wagon, as there were no mountain ranges in the Midwest to cope with and if one was willing to wait for spring, the towns were close to the border of what was then American prairie, as that started in Illinois.  Commerce and close proximity to grazing land were the reasons the "jumping off points" for the westward trails existed.