Black Gold — Dale Graham

After being paid for delivering horses to the army, Del Gannon and his partner Johnny stop off in Yuma. Del wants to quit the bronc-busting business and buy an orange farm in California. However, Johnny is robbed and killed while holding the money, leaving Del bent on revenge. Finding the killers, he rescues a young Indian, Lone Wolf, from their clutches and receives some mysterious black stones in return. What part could these stones possibly play in bringing Johnny's killers to justice...?