Forrest Fenn has written two books related to the search for his treasure, the first book, The Thrill of the Chase, launched the chase in 2010, it is his memoir and the essential guide book for the chase.  The second book, Too Far to Walk, came out in the Fall of 2013.  I have not purchased it yet, so can not say much about it other than that it builds on the first book, with more stories of his life, and more hints concerning the treasure.