Bryce Cardigan returns home from college to find that the beautiful glade named "The Valley of the Giants," where his mother is buried, is in danger of being taken from his nearly blind and financially troubled father. Cardigan, who built the nearby town of Sequoia, may lose the property to rival lumberman Colonel Pennington, an unscrupulous Easterner. Discovering that the giant tree guarding his mother's grave has been felled by Pennington's foreman Jules Rondeau, Bryce thrashes him. Although Bryce saves Pennington and his niece, Shirley Sumner, from death in a runaway logging train, Pennington ungratefully refuses to haul the Cardigans' logs on his railroad. With railroad agent Buck Ogilvy, Bryce pretends to build a new railroad to connect with the transcontinental line. After they find backers interested if they can cross the Pennington tracks, Shirley, now on Bryce's side, helps them secure the important franchise. Although Pennington tries to bribe the mayor, his dishonesty is exposed, the valley is kept in the Cardigan family, and Bryce and Shirley marry.