LeRoy Hafen, The Overland Mail: 1849-1869 (Originally published 1926)
Hafen’s book, which grew out of his doctoral dissertation, is the pioneering work on overland mail in the trans-Mississippi west. This is the book that all subsequent books cite. It is essential reading in understanding the developments that led to the Pony Express, and more. As the author states, “There is perhaps no better register of the growth of our country than the record of the expansion of the postal service. The opening of a post office in some remote section of the West is proof sufficient of the presence of the pioneer. The establishment of a post road is the official marking of the pioneer trail.”
In addition to being informative, it is eminently readable. Hafen’s style is a little dated, but it is not overly academic. I would write more a a review, but the bottom line is that this is a book well worth reading.