Two-Fisted Stranger (movie, 1946)

Arriving to become the new Deputy, Steve Gordon takes over as Sheriff instead when he finds the Sheriff has been killed. He doesn't last long and is fired for incompetence. But he realizes Brady is pulling off a swindle. Having found the proper soil, Brady has salted it with cheap diamonds, gotten Smiley to accidently find them, and is now taking money from eager investors and planning to flee with it.