The distance between Jeff's hand and his six-shooter on the bar changes between shots.
At Jeff's trial in the saloon, the items on the table keep changing positions between shots, among other inconsistencies.
The populace of Dawson City (or any Canadian city) never elected a U.S.-style marshal with tin star to police the city. The Mounted Police were present in the Yukon in large numbers before and during the Klondike gold rush to enforce the law.
There were no gunslingers or shootouts in Dawson City during the Klondike gold rush. The Mounted Police were in the Yukon in large numbers and enforced the law very strictly. Dawson City during the Klondike gold rush was peaceful and not lawless as depicted in the movie.
The film takes place in 1896. Ronda Castle contracts Jeff Webster to drive her caravan until Dawson, Canada. Nevertheless, that Canadian miner town-site was named Dawson only in January 1897.
When Jeff and Gannon have their shoot-out near the end of the film, Jeff gets off eight shots with his "six shooter" without reloading. Jeff actually fires nine shots, but at one point he is hidden behind the porch and could have reloaded, like Gannon is seen doing.
At about 19 minutes in Gannon slides a gun along a bar counter, after the camera cuts the gun points the other way. However, as the gun is sliding along the bar counter, it spins 180 degrees causing it to face in the opposite direction.
In a climate where there is snow on the ground the characters are seen wearing costumes worn in warmer temperatures.
The opening credits are played over a photo of the Athabasca Glacier. An ice road can be seen across the bottom of the screen, leading from the lake at the bottom right and winding off into the distance at the left. As the road turns you can see an automobile. The same photo can be seen shortly after crossing the border.
After the clubbing of the sheriff while James Stewart is standing in the door of the Dawson Castle. Modern brass hinges can be seen on the doors of the saloon. Since this was before the city of Dawson was founded in 1896, any hinges on doors would be wrought-iron at best.
Ruth Roman hides James Stewart in her bed on the paddle steamer. When she gets out of bed and stands in front of a mirror it can be seen that the back of her slip has a zip in it long before they were invented.
It was impossible to drive cattle overland from Alaska to Dawson City. There was no route over the mountains that cattle could follow.