Badland imagery
The imagery of the book that is most obvious is that it is set in a desert, away from other communities. It is its own country, and it isn't a nation-state in the regular sense of the word. Instead, the novel portrays Opium as a badlands where the law has returned to a Wild West law where the survivor gets to say what is just. It is each man for their self, and the people at the bottom of the social ladder see the injustice clearly, while the privileged few struggle to admit that anything is wrong at all.
Post-Apocalyptic Government
There are concrete and abstract uses of imagery pointing toward this concept of doom, apocalypse, and religious judgment, all in tandem with government brokenness. This imagery is a motif of the genre, and like sci-fi (which uses fantasy to illustrate truthful ideas), this post-apocalypse is both something that hasn't happened yet, and something that does happen all the time. The use of genre imagery in the novel helps the reader to see that this novel is criticizing present-day situations by drawing them out to their conclusions.
Drugs and addiction
Though subtle, the novel is clearly making an argument that drug addiction in Mexico and America is leading to an instability in the Mexican government because of cartels who gain money by exploiting that addiction. The town is called Opium, and the book ends with the cartel overlord using an addictive drug, alcohol, to kill his community by poisoning them. The money that fuels the powerful government comes from selling the community drugs that will make them pleasured and powerless.
Death and political abuse
Death imagery is partnered with political abuse, because El Patron is avoiding death by abusing his political power, and since he has continued to age, he is a gnarly sight to behold. He represents death to his community because he kills people. He kills his own sons, his clones, to harvest their organs, and in the end, when the community attends the funeral of El Patron, he kills them all from the grave with poisoned wine.