In relation to arguments, what is fallacious reasoning?

In a broad sense, all logical fallacies are arguments in which a conclusion doesn't follow logically from what preceded it. Or that the conclusion is produced by an argument that is not based on a strong and logical basis.

In regards to linguistics, there can be:

A semantic fallacy is a semantic error in the mistaking or confusing of the current meaning of a word with the meaning of one of its etymons, or of considering the meaning of the etymon to be the "real" or "true" meaning of the current word.

A logical fallacy is an error in reasoning that males an argument invalid. They are the most common and seen kinds of fallacies.

A normative fallacy happens when someone argues that something is not the case or is the case based on a set of ideological, ethical, moral, political, or other normative commitments.

In regards to general reasoning there can be:

Hasty generalization: Making assumptions about a whole group or range of cases based on a sample that is inadequate.

Missing the point: The premises of an argument do support a particular conclusion—but not the conclusion that the arguer actually draws.

Post hoc: Assuming that because B comes after A, A caused B

Slippery slope: The arguer claims that a sort of chain reaction, usually ending in some dire consequence, will take place, but there’s really not enough evidence for that assumption.

Weak analogy: Many arguments rely on an analogy between two or more objects, ideas, or situations.

Appeal to authority: Often we add strength to our arguments by referring to respected sources or authorities and explaining their positions on the issues we’re discussing.

Ad populum:  The arguer takes advantage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument.

Ad hominem and tu quoque: Like the appeal to authority and ad populum fallacies, the ad hominem (“against the person”) and tu quoque (“you, too!”) fallacies focus our attention on people rather than on arguments or evidence.

Appeal to pity: The appeal to pity takes place when an arguer tries to get people to accept a conclusion by making them feel sorry for someone.

Appeal to ignorance: In the appeal to ignorance, the arguer basically says, “Look, there’s no conclusive evidence on the issue at hand. Therefore, you should accept my conclusion on this issue.”

Straw man: In the straw man fallacy, the arguer sets up a weak version of the opponent’s position and tries to score points by knocking it down.

Red herring: Partway through an argument, the arguer goes off on a tangent, raising a side issue that distracts the audience from what’s really at stake. Often, the arguer never returns to the original issue.

False dichotomy: In false dichotomy, the arguer sets up the situation so it looks like there are only two choices.

Begging the question: An argument that begs the question asks the reader to simply accept the conclusion without providing real evidence; the argument either relies on a premise that says the same thing as the conclusion, or simply ignores an important (but questionable) assumption that the argument rests on.

Equivocation: Equivocation is sliding between two or more different meanings of a single word or phrase that is important to the argument.

So, to sum all of this information, In relation to arguments, a fallacious reasoning is:

Arguments in which a conclusion doesn't follow logically from what preceded it. Or that the conclusion is produced by an argument that is not based on a strong and logical basis

alright, so here, the author clearly thinks that flooding the canyon was a bad idea and is showing bias against it.

the answern should be b, if it is the part where the mob has gathered