The Pengra Pass rail route, also known as the Natron Cutoff, the Cascade Subdivision, or the Cascade Line, is a Union Pacific Railroad line (originally a Southern Pacific Railroad line) connecting Eugene, Oregon, with Klamath Falls, Oregon. Construction of the line began in 1905 and was completed in the mid-1920s. Its name denotes a mountain pass on the Lane County-Klamath County boundary in the Cascade Mountains of Oregon, about from Willamette Pass. The line heads southeast from Eugene, up the Cascades and over Pengra Pass, then southward beside U.S. Route 97 to Klamath Falls, where it splits in two, each track continuing into California. The route has at least 22 tunnels, several snow sheds and multiple bridges across canyons.