Soon after the drive begins, Ben is telling the cook why he wants to be a cowboy. The camera is in the wagon, behind them, and the sun is about to set behind a mountain. The cook says "Kid, cowboying is something you do when you can't do nothing else." Immediately thereafter, there is a camera change to a shot showing the wagon approaching the same mountain, but the sun is much higher in the sky. Maybe an hour before sunset.
Immediately after starting the drive, the cook needs to spit, and does so across Ben, who is sitting beside him. The cook then tells Ben that he better "Sit down wind." This is wrong, because Ben should sit Up Wind. You never spit Into-The-Wind, you always spit With-The-Wind or Down Wind. The line should have been, "You better NOT sit down wind."
In cattle drives, the chuck wagon often went ahead and set up to have dinner ready for the cowboys when they arrived. If the cattle were driven from dusk to dawn, the chuck wagon drove until an hour before dusk, and then stopped to cook, and await the arrival of the herd. If the drive was of predetermined length, the wagon went ahead still, always prepared ahead of time, because cowboys were expected to work right up until the dinner chime. There was never down time with the sun up.
The story line is of a cattle drive in 1866 north from Texas to Colorado. As there were no direct railroads from Texas to Chicago (the eventual destination for these cattle), cattle drives took cattle north to Kansas, NOT Colorado, where the railroad heads (the end of the railroad line) were located in the mid 1860s. Town like Dodge City and Abeline sprang up at these railroad heads as the railroad continued to move west toward Promontory Point in Utah (the eventual meeting point of the Union Pacific and Central Pacific railroads in 1869). These towns WERE the destination for cattle drives where stock buyers would give the cattlemen top dollar for their cattle and ship them back east to Chicago. It would have made NO sense to drive cattle past these towns in Kansas to get to Colorado. Doing so would have caused the cattle to become leaner and therefore less valuable.
Ft. Lewis, Colorado existed from 1878 until 1891. The film was set in 1866, meaning that it would be more than a decade before the fort was constructed.
With a single exception, all of the firearms shown and used were of 1870s or later manufacture and would not have been available to the cowboys.
Another anachronism is a pressure lantern (invented in the late 1890s) visible in one bar scene.
During the final shootout, a cowboy clubs another from horseback using a rifle and the arresting cable to prevent the cowboy from falling under the horse can be seen.
The story line is of a cattle drive north from Texas to Colorado. But when the dust storm hits, saguaro cactus can be seen. Saguaros are located in the Sonoran Desert which is in Southern Arizona and Northern Mexico. This is west of Texas and no cattle drive from Texas to Colorado would go west and only have to go east again to get to Colorado.
When Ben begs to be allowed to take a turn watching the cattle, he puts his gun on, and tries to do some fancy gun twirling. He knows enough that a gun-slinger wears his holster low on the hip at arms length, yet he fails to perform an important function of tying the holster down. Any kid who carries a gun, yearning to use it one day knows what the strings are for and how important they are. He wouldn't forget to do this, because his gun could bind during the draw. He can't wait to strap it on and tie it down. You tie them standing up, not after you get on the horse.