Factual error: We see how the accident-prone Wilton Parmenter was a soldier at Appotomatox during the Civil War when he sneezed. Union soldiers mistook his sneezing for a call to regroup and charge, winning the battle. Wilton Parmenter was awarded the Medal Of Honour. Accident-prone, even in his moment of glory, when the medal was pinned on Wilton's chest it pierced his skin, drawing blood. Wilton was therefore awarded the Purple Heart, becoming "the only soldier in history to get a medal for getting a medal." This was not possible, for the "Purple Heart" (or "Badge Of Military Merit", to use its proper title) awarded to US soldiers wounded in action, was only instituted in 1932. (Before somebody corrects me, George Washington did institute the award for some distinguished combatants during the War Of Independence, but it was never awarded during the nineteenth century, and revived in 1932).
Continuity mistake: When the Indian agent is killed, a very 20th Century rubber-tread shoe print is visible in the dirt beside him. When Cheyenne arrives and finds the body, though, the footprint has disappeared.
Old Scores - S2-E17
Continuity mistake: In the scene where Shaddock is shot in the arm you can see that the wound moves from near his elbow to his shoulder.
Other mistake: The Lakota is attacking a small group of white men. One is face down on the ground, and he lifts his head to cut his throat. In the background are two cowboy actors joking and twirling their guns. One drops their gun and picks it back up. (00:20:43)
The Crossing - S1-E4
Factual error: The Dutton camp as well as Shea Brennon and Thomas are using modern thin Teflon/non-stick coated coffee mugs/pot.
Visible crew/equipment: As the old Indian sets fire to burn his dead son, he walks towards Cain and on the left you see a fire extinguisher. (00:10:04)
Other mistake: José accidentally drops a cake containing hidden explosives. Pat accidentally drops a cake containing hidden explosives. Both scenes use the same close-up footage of an explosion. (00:00:23 - 00:01:05)
The Town That Wasn't There - S4-E3
Continuity mistake: John Astin, playing a homely sheep farmer, wears a large fake nose throughout the episode. But in the saloon meeting scene, where Beau introduces him to the townsfolk, the nose is conspicuously missing.
Visible crew/equipment: When Bat arrives at the hotel to escort Lucy, the shadow of the microphone and part of the boom rigging are visible on the wall above the door. (00:17:30)
Character mistake: When the gang is watering the horses, Chris walks over to meet Mary's man friend (whom she introduces as an old friend of the family) and the mystery man tells Chris that he'd proposed to Mary long before 'Frank' when Mary's late husband was Steve.
Continuity mistake: During the ambush, young Jack, on horseback, takes off after the wagon which is carrying his wounded fiancé. The chase is long including a cut away and yet the wagon winds up only yards away from the ambush where the chase began.
Continuity mistake: Conchita slaps Cash across the left cheek, which he's rubbing as he returns to his office. In the next shot, as he comes through the door, he's rubbing his right cheek instead.
Adios, Señor Magistrado - S1-E26
Character mistake: During the tavern meeting, Sergeant Garcia calls Magistrado Carlos Galindo "Comandante."
Factual error: The show is set in the 1860s. However, in several episodes, trail boss Gil Favor can be seen wearing Wrangler jeans. The Wrangler brand was not introduced until 1947.
Factual error: In this final made-for-TV mini-series of the 'Lonesome Dove' franchise (the one with James Garner as Woodrow Call), they show the crazy renegade teenage killer hanging Judge Roy Bean from the beams outside the front of his own store/courthouse. Bean died peacefully in his bed on March 16, 1903, after a bout of heavy drinking in San Antonio.
Factual error: Two women come into town somewhere around San Luis Valley, Colorado with ring-necked Pheasants. The pheasants were brought into US a few times (East coast, CA) but really did not get established until late 1880s and in Colorado likely in the late 1890s (eastern and southwestern). The problem is it supposedly depicts the year 1880. They would more likely may have found some Gunnisons Sage-Grouse nearby or rabbits. (00:16:10)
The Kid from Silver City - S3-E10
Continuity mistake: Roy is visited by a deputy marshal who is looking for the son of a local storekeeper. When the two men leave to visit the storekeeper, Roy leaves his hat on the kitchen table, but when he enters the store the hat is on his head.