LeRoy R. and Ann W. Hafen
The Hafen's book is the most fundamental reference on the Old Spanish Trail. Although somewhat dated, it remains the one book that any serious student of the trail must have. Unfortunately, it is out of print, although it can be obtained from antiquarian dealers from time to time.
The book reviews the history of the trail, sets its historical context, includes much of the material found in the few specific contemporary references on the trail and its travelers, and provides chapters that confer substantial insight into the mechanics of moving goods on the backs of mules about 1200 miles through very forbidding terrain
