Not a full historical background, but Under the Banner of heaven is excellent

A pretty good exploration of the events that lead to Mountain Massacre is Blood of the Prophets: Brigham Young and the Massacre at Mountain Meadows by Will Bagley.

Another good one is Kingdom of Nauvoo: The Rise and Fall of a Religious Empire on the American Frontier by Benjamin E. Park.

The Mormon Church has had a pretty active marketing and PR arm going back a long time, so most of the books are very complementary of the "American Moses" and skip over more controversial historical datapoints.

You say "Sordid history" though, and I do admit a bit of sympathy for the Mormon settler. Not because of their foolish claims to to the Utah territory and not because of their belief in polygamy etc etc. but because their acts of violence did not rise out of a vacuum. They were attacked and killed pretty much everywhere they went and the formed militias in response.

Second to Windy's first recommendation.

If you want to mix your Mormon study with Texas History and the Civil War, read Charles Roland's biography of Albert Sidney Johnston. It has a pretty long chapter on the Mormon War that explains the pre- and post- war history. Johnston commanded the army troops sent to Utah.

Georgian Alfred Cummings was the territorial governor after the war and accompanied Johnston. He is one of the unsung heroes of American History. Through skilled diplomacy and with the assistance of his highly intelligent wife, he got the whole mess settled and got Utah on the path to full integration with US society.

If you want to deep dive into the origins of Mormonism, The Mormon Enigma by Newell is an interesting read. It is basically a biography of Joseph Smith's first wife. It is not kind to the Mormon faith, but follows the history of Mormonism from its origin until the exodus to Utah.

This was one of the required reading books for the History of American Religion class I took at A&M.