The Iron Trail.

Alaskan railroad magnate Curtis Gordon hires engineer Dan Appleton to design a railroad route up the Salmon River to the rich gold country. Gordon turns down the engineer's proposed route in favor of his own, and Appleton quits. Murray O'Neil, a rival builder, hires him and falls in love with his sister Eliza, while Appleton courts Natalie, Gordon's stepdaughter. Following Appleton's plan, O'Neil lays the trail with a bridge crossing the river in face of Gordon's opposition.