Face of a snake : a Ralph Compton western
(Book)

"The law only caught up with the Venom Snakes and their bitter rivals, the Red Trail Gang, because they were so busy killing each other. Now, after twenty years in prison, Ashford Sinclair is broke and broken. Without his gang behind him, the once fearsome leader of the Snakes is reduced to eking out a solitary living as a fur trapper. One day, news comes that his son William has married the daughter of Henry Odell, erstwhile leader of the Red Trail Gang. Furious at his son's betrayal, Sinclair vows he'll never speak to him again. But when William is murdered in a land dispute and a gang of hired guns starts threatening his grandson next, Sinclair has no choice but to join forces with his most hated enemy--as the two outlaw grandpas ride for justice!"--Amazon