Trans-Mississippi mythologies

In this recent post, Jane Johansson cites a recent book release and adds a Trans-Mississippi perspective to the more general problem in Civil War historiography (or really any historiography) of uncritically perpetuating unsubstantiated views found in supposedly authoritative secondary print sources.

She asks "What “facts” do we read time and time again in secondary sources about the trans-Mississippi? Are they really true?" Jane offers an example, the theater's reputation as a backwater of military incompetents and dumping ground for eastern command failures. In coming up with one of my own, I should really be on the ball and quote directly from some of the relevant secondary sources, but I'm sure most readers have already come across the oft repeated notion that the northern victory at Pea Ridge was the defining event in securing Missouri, or even more fantastically -- St. Louis, for the Union. In truth, while the Confederacy and its local adherents could always threaten the state on a temporary basis, Missouri was in the permanent grip of the U.S. military ever since Lyon's summer 1861 campaign, long before Pea Ridge. Nothing resulting from Pea Ridge could have changed that. With none of the state's railroads and deeply penetrating rivers connecting to Confederate sources, those who repeat this idea of the battle's strategic import seem not to have considered the logistical impossibility of maintaining a sizable Confederate army in Missouri. This inability to seize and hold even remote swatches of Missouri territory for any significant length of time would be demonstrated throughout 1862-64.

Does anyone else have a favorite T-M head shaker?