Based on Peter B. Kyne's novel, a greedy businessman tries to log the redwoods, but a local mill-owner fights to preserve the forest.
In 1902 Howard Fallon (Charles Bickford) and his lawyer Hendricks (John Litel) in Milwaukee plan to steal timber legally from California. Fallon offers Lee Roberts (Claire Trevor) $5,000 to go and set up a gambling house to collect the money he is paying men to use to buy land. Bill Cardigan (Wayne Morris) fells a redwood that almost hits the wagon of Lee and Ed Morrell (Jack La Rue). Cardigan guides them to San Hedrin, where Sheriff Graber (Cy Kendall) welcomes them and gambler Fingers (Frank McHugh). Cardigan owns the mill, and Lee goes fishing with him. Cardigan says he won't cut down the giant redwood trees. Fallon arrives with lumberjacks. Lee tells Fallon about Cardigan. Fallon offers to buy the valley of the giants, but Cardigan won't sell. Fallon takes over land and ejects homesteaders. McKenzie (Russell Simpson) refuses to leave and is knocked out. Ox Smith (Alan Hale) tells Fallon that he quit. Cardigan and Andy Stone (Donald Crisp) persuade residents to talk with Hendricks, who is defended by the sheriff. Cardigan lets Ox stay in his place and goes to Sacramento, appealing to the Forest Commission.
Fallon's people arrive on a boat to file land claims. Andy complains to Hendricks that no notice was given. State land is sold. Cardigan argues with Fallon and tries to stop the sales but is beaten up. Cardigan tells Andy his land can keep Fallon from logging, but Lee told Fallon about his $50,000 bank loan. Lee warns Cardigan that Fallon will kill him and advises him to sell; but Cardigan rejects her for helping Fallon. In the gambling hall angry Ox socks the sheriff and fights several men. Cardigan comes in and fights too. Cardigan tells Ox the claims are in the land office and goes to sleep. Ox burns down the land office. Fallon tells Andy he wants to buy Cardigan's note, but Andy denies the note. Fallon has him audited and charged with embezzlement; so Cardigan tells Andy to give Fallon the note. Fallon tells Cardigan he has six weeks to pay it.
Cardigan plans to log and asks for help. Lumberjacks cut down trees and transport them by rail and water. Fallon plans to sabotage the railroad, and Lee tells Morrell she will warn Cardigan. Saboteurs are chased away by Cardigan. Lee and Fingers tell Ox of Fallon's plans, but Ox locks them in the caboose. Men release the brakes of the train. Cardigan heroically stops the caboose while log cars collapse the bridge. Cardigan tells men to get dynamite to keep Fallon from damming the river. Lee says she changed, and Cardigan kisses her. McKinzie shoots three men and draws fire while Cardigan and others place explosives to blow up the dam. Fallon and Cardigan fight. Cardigan knocks Fallon into the water and saves him from the explosion. Fallon thanks Cardigan and decides to leave, letting Cardigan keep his land.
Spectacular color shots of the redwoods and logging action highlight this conflict between a ruthless manipulator and a mill-owner who intends to log intelligently in order to preserve the forest. Despite the power of money and official corruption, the homesteaders join together to defeat the exploiters, though the killing by McKinzie is egregious.