This nice Sunday afternoon read (just 96 pages in the original), available on Project Gutenberg, offers a straightforward history of the Battalion.
It’s especially interesting in that it gives good background of how and why the Battalion came to be formed – turns out the Church actually asked the government for a way to serve in the West (originally expecting to build forts or supply posts, etc.). At around that time, the Mexican-American war happened, and the Church’s agent in D. C. agreed to the idea of the Battalion. After getting government permission to be on Indian land (more or less in exchange for the Battalion) Brigham Young supported the whole thing. I once had an impression that levying the Battalion was something of an oppressive act by the government; though it was a sacrifice, the real history’s more nuanced, and it was a mutually beneficial arrangement.
It then traces the route and history of the Battalion and discusses its significance, including the Battalion’s road-making, its members’ roles in starting the California gold rush, the record-making length of its journey, etc. Roberts also says:
Commenting on the Battalion’s march and the map he made of it, Colonel Cooke says: “A new administration, (this was the Pierce administration, 1853-1857) in which southern interests prevailed, with the great problem of the practicability and best location of a Pacific railroad under investigation, had the map of this wagon route before them with its continuance to the west, and perceived that it gave exactly the solution of its unknown element, that a southern route would avoid both the Rocky Mountains and Sierra Nevadas, with their snows, and would meet no obstacle in this great interval. The new ‘Gadsden Treaty’ was the result: it was signed December 30, 1853.” This purchase added to the territory of the United States forty-five thousand five hundred and thirty-five square miles; for which was paid $10,000,000. The purchase was made by James Gadsden of South Carolina, minister to Mexico, hence the name Gadsden Purchase.
So, arguably Tucson (inside the Gadsden Purchase area, along with much of southern Arizona and New Mexico) is part of the United States because of the march of the Mormon Battalion. Anyways, it’s a quick read that will cement the history of the Battalion in your mind and has a number of fun tidbits; I recommend it.