These two titans are not the only dramatis personae of Groom’s vivid account. Other principals include the Mormons, then in quest of the Zion they would find in Utah, beyond the hostile reach of the United States. And the tragic Donner party, who set out on bad advice to cross the Sierra by a shortcut called the “Hastings Cutoff.” They were trapped in the passes by early snows and their fate is gruesome and legendary. Groom calls his account of that fate “The Horror,” echoing the last words of Conrad’s Kurtz: a figure of fiction who exemplifies the pressure of unfriendly nature and isolation on civilized norms. Groom writes:

On .  .  . the same day .  .  . Kearny marched victorious into Los Angeles, Luis and Salvador, the two Miwok Indians accompanying [the Donner travelers] in their attempted escape from the Sierra, were killed and eaten by starving members of the party.

As that stark sentence suggests, Groom’s retelling of the Year of Decision is brisk, unblinking, unsentimental, and sometimes grim. And appropriately so. This is not a tale for dainty or euphemistic narration, and Groom knows warfare at first hand. The story is all too human, marking our perennial capacity for good and evil, the heroic and the shameful, the tragic and the triumphant.

Edwin M. Yoder Jr. is the author, most recently, of Vacancy: A Judicial Misadventure.