The Ferguson rifle - Louis L'Amour

It began with gold that had once belonged to Montezuma. Stolen and cached in a church
in Mexico, it was recovered by two army officers who fled north for the French settlements.
Along the way one stabbed the other to death. The remaining officer was eventually
killed by Plains Indians, but he buried the treasure just before he died.

Now Ronan
Chantry, a handful of trappers, and an Irish girl whose father was killed after telling
her a few vague landmarks are searching for the lost treasure. But they are not alone.
The girl's uncle, Rafen Falvey, wants it, too. Like Chantry, he is well educated,
bold, and determined. Under different circumstances the two men might have been friends.
But in all likelihood it wouldn't have made any difference. When it comes to gold,
even friendship doesn't keep men from killing each other.