This fourth expedition was an attempt to find a pass through the central Rocky Mountains in the depth of winter, the one failure of a great explorer, and the cause of some of the most savage suffering men have ever endured. The author's interest seems to center too much on the men who formed the party and the wilderness they traversed, and in this he succeeds at the expense of delaying the march of events. Fremont organized this winter expedition after his court-martial. He was cashiered from the Army as an aftermath of his freebooting expedition in California. Caught between the aspirations of General Kearny and Commodore Stockton as they rowed over supreme command and the spoils of war, Fremont was sacrificed. To vindicate himself, and perhaps to please his new father-in-law, Senator Benton, Fremont once more set out for the West. His personal motivation was perhaps too shallow to carry the party through the awful hazards. Or perhaps the mountain winter was just too much for men and mules. Whatever the reason, the expedition failed. But the members sensed their place in history and left individual records, and out of these journals and a host of other material, Brandon has documented his account. There are rare spots that will be long remembered, such as the tongue in cheek step by step description of the workings of the mind of a mule. Perhaps this may capture some segment of the market of the mountain fraternity.