"Parlor entertainment" using a variety of literary devices in the crafting of this otherwise fictional tale....OK....let's run with that. First order of business is in explaining how this author knew about those two sources of wealth from the Texas region when this information wasn't public until the mid/late 1940's, and there can be no mistaking, he clearly knew about them. So, how did he know? Let's explore this.
Well, he could have read the "highly questionable" memoirs some 60 years prior to their being made public? Or, perhaps he actually spoke with someone who held first hand knowledge of those sources of wealth from the Texas region? Or heck, given enough good health he might have actually been a part of those events himself? So what you say, how did he know, because very clearly, he did know.

You tell me.

And if you think this is all I have for you then you are badly mistaken.