Near the middle of the movie, the wagons filled with supplies for the settlement have stopped to "noon" just above the tree line. Just as Glyn rides up to get a cup of coffee, there are a series of what look like power poles or telephone lines at the left side of the screen on the horizon.
Near the beginning of the film, while camped very close to the base of what is obviously Mt Hood, Jimmy Stewart's character says they are heading for a place 150 miles east of Portland. Mt Hood is only 50 miles east from Portland. Not only that, but they go through Portland on their way to their settlement.
After dropping off a party to cross over Mt Hood, the paddle wheel captain indicated that he was taking the boat back to the Mississippi river. This would entail going all the way around South America. A paddle wheel boat would not be capable of such a journey.
At the base of Mt Hood, the settlers are attacked by a band of Indians that the trail guide declares are Shoshone. Although there were Shoshone (Paiute) tribes in southeast Oregon, Mt Hood is in north central Oregon along the Washington border - too far to the northwest to have been on any Shoshone ground.