Irony of Hell Creek
Hell Creek is an ironic place; it is a road that leads to Memphis, but the catch with it is that it's mudded completely by the mule workers and it makes cars unable to go through there alone. We come to find out that the mule workers make that path impassable intentionally so that the drivers are forced to pay them for their help. Looking at it objectively, it is a genius method because it is the easiest and highest-paid way for the mule workers to make money.
Boon's irony
Boon is brave and honest and loyal, but completely unreliable. He is a hugely grown man with the mind of a child. Lucius notices that when they start the car to go to Memphis, Boon seems to be relying on his, Lucius's, consciousness and willpower to tell him to turn the car back home before it's too late. Lucius, at eleven years old, shows a higher sense of maturity than Boon. He sees the faultiness and unhappiness of Miss Corrie and wants her to be better, to decently work for herself, while Boon only wants from her what he made the long trip for. Ironically enough, even after hitting her, Boon ends up marrying Miss Corrie.
Irony of the ending
So what happened at the end? Lucius goes back to his usual life. He expects a punishment for what he's done, but, and this is what his grandfather realizes, the reality of having to face and live with the knowledge is punishment enough for the boy. Some time passes and he goes to meet Miss Corrie's baby. He doesn't think much of it, only that it already looks as ugly as Boon, but guess what? The baby's name is Lucius Priest.
