Kal Emerson and his pal, Steve Sloan, come to the town of Challis to try to get a backer for them to prospect for gold. According to an Indian who drew up a map for them, the mountain where the gold lays buried long ago gave up rumbles like thunder, whereupon the Indians, figuring that it was angry with them for taking its gold, pulled up stakes and left. Despite the warnings of Nugget, a dance hall girl who loves him, Kal tries to interest Rand Leavitt, who has control of the town. After Kal helps pretty Sydney Blair dispose of a drunk from her hotel room, her father invites him and Steve to breakfast and then agrees to stake them to $300 for one-third interest in their find. After Kal and Steve strike the mother lode, Kal sends Steve back to Challis to file the claim, while he goes to tell the Blairs, who have since returned to their home in the town of Salmon. In Challis, Leavitt and his cohort, Cliff Borden, waylay Steve before he can file the claim. Kal and Sydney fall in love, and when they get to the mining area, they discover that Leavitt has filed the claim. Sydney believes Leavitt's story that a man whom he grubstaked located it two months ago. Leavitt offers her and her father, who still believes in Kal, an interest in his claim, while Kal vows to find Steve and prove that Leavitt jumped the claim. Leavitt proposes to Sydney, and she agrees to marry him after she sees Kal with Nugget. Kal gains the confidence of some miners who are disgruntled with the way the Leavitt-run miner's court has decided their claims. Steve returns to the camp and reveals to Kal that Leavitt and Borden knocked him out, and that he regained consciousness in the desert with a broken skull. After he was picked up by people travelling in a wagon, Steve recuperated and made his way back. Kal hides Steve in the tent of Foley, a friendly miner, and plans that night at the miner's court to have Steve appear and tell his story, but Sydney overhears Kal tell her father about Steve, and she tells Leavitt. When Steve does not appear at the meeting, Kal finds him wounded, and before he dies, Steve says that Leavitt knifed him. When Foley warns Kal that killing Leavitt would be murder, he gives Leavitt until noon the next day to leave the camp. The next day, Borden, fearing Kal, tells Leavitt that he is leaving and starts taking his share of the gold already mined. When Leavitt orders him to leave empty-handed, Borden threatens to tell Kal that they jumped the claim, so Leavitt shoots him. Borden revives, however, and reveals that Leavitt shot him and that they jumped Kal's claim. Leavitt then leaves the camp and hides his gold, as Kal, alerted by Sydney, follows. Leavitt climbs "Thunder Mountain" on foot, but Kal jumps him and they fight. Leavitt slugs Kal but slips trying to get away and falls off the cliff. Sydney then tries to revive Kal's interest in her, but he rebuffs her; however, Foley later sees Kal and Nugget embracing and says, "It's about time."
