Continuity mistake: There are seven Wharvey Gals. Three on the stage singing, three with the wife, and one that she's holding. One of the girls even says that there are seven of them. Yet in the end, when Everett and his wife are walking down the street, there are only six. One that she is carrying, and five following.
Plot hole: Near the beginning of the movie, one of the characters states that it is the 17th and the valley would be flooded on the 21st. Yet, throughout the movie, there are too many nights that go by for it to just be the few days when the valley finally floods.
Continuity mistake: When they first meet George Nelson, the left back seat window is half way open. A few seconds after they get into his car, Delmar gives the machine gun to Nelson through the left back seat's completely open window (the camera shows the guys all the time so we can see that Delmar didn't lower the window when he got in the car).
00:32:25 - 00:33:40
Continuity mistake: In the scene where Everett finds his wife in the Woolworth's, he pulls her off to the side to have a private conversation. You can see the twine that connects her and all her children start to stretch out as she walks away. In the next shot, as she is walking over to Everett, the string is gone.
Continuity mistake: In the scene near the beginning where the three main characters are running across the field to catch the train, in the shot where the train is in the foreground you clearly see the engine and the front carriage pass by the convicts while they're still quite a long way from the train. In the next shot though which is taken from behind the men with the train in the background they reach the train pretty much as soon as the engine passes them by.
Other mistake: The radio station had no power or telephone lines anywhere in the vicinity, and the lines would not have been buried in 1937. A telephone is seen on the wall inside the building, yet it couldn't have been connected to anything. There wasn't a generator to power the radio transmitter, because it would have had an exhaust pipe through the roof, nor was there any adjacent building to house a generator.
Continuity mistake: When Clooney and the 2 other guys enter the political meeting, there's a close shot of Clooney where he addresses Hunter. Meanwhile, the music is playing and the others are singing. Behind Clooney you can see, out of focus, a man playing a guitar along with the music. When the music stops, we go back to Clooney's close shot (where he is still talking to Hunter) but the man behind him is still playing the guitar.