When John and Buck started to row down the river, John had the backpack and his rifle with him. The backpack and rifle were still on the boat before the cascade. When they managed to surface from the cascade, the backpack and rifle were gone. But after they left the boat, John had them both with him.
The contents of Hal's sled varies between shots. When we first see the sled, there are 4 distinct brown-tinted suitcases. When Hal departs, we only see 2. When Thornton confronts Hal on the hill, there are 3.
Buck's eyes never move like a dog's eyes, and he continually reacts to the world around him as though his primary sense was sight, when it should be smell.
The river has a rather thick layer of ice. However, it has such a strong current that it would be impossible for ice to form on it.
There have never been pheasants in the Northwest Territory or Alaska although they appear at about one hour and 16 minutes mark when Buck and the wolves kill pheasants.
In the 18th minute, Dawson City in the Yukon Territory city in Canada is incorrectly referred to as Dawson.
When Thornton's canoe springs a leak, the water is shown to spurt above the level of the gunwales. Boats to not leak like that. It is impossible for the water to exceed the height of the water in the river, since atmospheric pressure is the same on both.
The "Victrola" phonograph and the white crate of Moët & Chandon hitched to the front of the sled go missing when Hal reaches the hill. By this time, they could be presumed to have shed extraneous baggage and weight, in their struggle to proceed forward.
When John and Buck are rowing downstream at night, the reflection of the moon is seen clearly in the water, but it's not mirrored.
Valuable gold nuggets are surprisingly heavy to handle, but neither John (nor indeed Buck) are clumsy with the weight when fishing them out of the river bed.
The message on the telegram that Perrault receives has a uniformity and cleanness that demonstrates that this was produced not on a typewriter, but by a modern laser printer. Also, the telegram's text uses a modern Courier font not present on typewriters of that period.
The telegram that Perrault receives uses a company name and logo from the 1930s. In 1897, such a telegram form would be titled "The Western Union Telegraph Company." (period included) and not simply "Western Union". Also, on a true telegram, there would be several lines of routing information preceding the actual message; this telegram has only the date. Finally, the format of the date, "1897 Apr 4", is also irregular.
When Thornton is freeing the runners of ice, Hal shouts "Watch the Victrola!", referring to the delicate phonograph hitched to the front. However, the first Victor Victrola was sold in 1906 (this film takes place in 1897). In any case, the phonograph depicted is not a Victrola at all: it is an Edison "Model F" Standard Phonograph. However, the Edison would also be anachronistic, since this model was introduced in late 1911.
In the 1890s, business signs atop town store facades would still be using periods in the names displayed. So, for example, the signs would say "Barber Shop." and "Post Office." (using periods) rather than simply "Barber Shop" and "Post Office" (no period).
During the Yukon summer, it does not get dark at night.
Hal places a map up to the end of a waving curve casually drawn upon the floor, and uses this to find a small cabin in the vast wilderness taken over by John.
While writing a letter to his wife, Sarah, John Thornton writes the word "every" but says the word "each" in his voiceover.
In the beginning of the movie, a sign on a building in the background has "Groceries" misspelled as "Grocereries."