our course from thence would be westward through iowa bearing a little north until we came to the missouri river , leaving the state of missouri on the left , thence onward , until we came to the platte , thence up the north fork of the platte to the mouth of the sweetwater river in longitude 107 degrees , 45 minutes west ; and thence up the sweetwater river to the south pass of the rocky mountains , about eleven hundred miles from nauvoo ; and from the south pass , in latitude 42 degrees 28 minutes north , to the valley of the great salt lake , is about three hundred miles , making the distance from nauvoo to the valley one thousand four hundred miles .