The Utah War remains an understudied but important moment in western history as the United States wrestled with its political future. There are few primary accounts from this war, but one of the best comes from William Clark, a young teamster hired by Russell, Majors and Waddell, the West's greatest freighters. Clark's narrative, "A Trip Across the Plains in 1857," was not published until 1922 and only then in an obscure journal with little annotation, so for the last hundred years, this work has been a valuable but obscure document. In On the Overland Trails with William Clark William P. MacKinnon and Kenneth L. Alford have remedied this historiographical oversight by providing material entirely missing from the original printing, including an explanation of the Utah War's origins and prosecution; maps by which to chart Clark's travels; illustrations to enliven major players; and annotations to clarify the sometimes arcane people, places, incidents, and issues mentioned. Also included for the first time is an account of the manuscript's colorful provenance.