The Oregon TrailGoofs
Near the end during the big Indian attack, the soldiers blow up a wagon full of powder to deter the Indians. A few seconds after the 1st explosion, a slightly different camera angle shows a second explosion which is identical to the 1st. Although the wagon is fully engulfed in flames after these explosions, a minute later as the Indians retreat, the wagon is not on fire but on a subsequent shot, a small flame is now evident.
In the fight scene around the campfire between Fred MacMurray and another member of the wagon train, Fred's hat is definitely lost early in the scuffle. After landing a right jab and knocking his opponent down the camera cuts to the man on the ground and Fred (via his stunt double) leaps on top of him wearing his hat.
In scenes at the White House, President James K. Polk stands in front of a US map, but the map shows the US following the Compromise of 1850. The film is set in 1846, before the Texas border was changed, before the Mexican Cession resulted in the admission of California and the organization of the Territories of Utah and New Mexico, all of which are clearly seen on that map.