Mystery of Haddock's Gold

Estimate publishing year, not stated. Jack Westland's three sons were setting out for the summer vacation of their young lives. They built a play fort and were planning a summer at the fort that would challenge their imagination to its fullest. In the process, they discover artifacts from an unsolved gold robbery from the gold rush days. This gets the whole town of Mountain Ranch excited. But along comes a stranger and the three boys find themselves trapped between the evil of the past and the terror of the present, and to surive they must unravel the 140 year old Myster of Haddock's Gold.