Christopher Brown 
The Lost Treasure of the Mogollon Rim [PDF ebook] 

To get away from the daily grind, Tim Clarke takes up gold panning. In the process of researching locations for his new hobby, he discovers a forgotten newspaper story about a mysterious place containing lost bullion.
Taken under the wing by seasoned prospector Chance Owen, they strike out in search of the treasure. Their paths cross with Amy Standing, a young member of the local Apache tribe, whom Tim has amorous feelings for. Together with her older brother, David Standing, a man with invaluable expertise for such a quest, they set out to find the mine said to harbor the lost hoard of gold.
However, the journey is anything but easy. Putting great trust in one another, they carefully tread the backcountry trails, trying to stay clear of the authorities, the hazards of the abandoned mine, and a frightening native legend, which just might be more than folklore.