Miners and settlers began building more roads into the wilderness. The Goat Trail had a dangerous section known as the Devil's Corner, where a hanging bridge made of split logs traversed a narrow ledge.
In 1930, the Diablo Dam was the highest dam in the world (389 ft.). Ross Dam was completed in 1949 (540 ft.) and Gorge Dam (300 ft.) was completed in 1961.
Between 1925 and 1926, the waters of Lake Chelan were raised 21 feet by a hydroelectric dam which was built down in Chelan. The additional water would have flooded many buildings like the Field Hotel so they were dismantled or moved. Construction of major hydroelectric development of the Skagit River began in 1918, when Seattle City Light was issued permits to begin construction of three dams along the river. Seattle City Light eventually built a railroad up the Skagit Valley to its company towns of Newhalem and Diablo. A diversionary dam at Gorge Creek was completed in 1924, and Diablo Dam - at that time the highest dam in the world - in 1930. Ross Dam, dedicated in 1940, was raised in 1949 to 540 feet, making it the highest of the three dams providing power to the city of Seattle. Visible from State Route 20 between Newhalem and Diablo, the present Gorge Dam was completed in 1961.
The North Cascades Highway was completed in 1972. Closed in the winter, this scenic highway crosses two passes: Rainy Pass (4860 ft., 1481 m) and Washington Pass (5483 ft., 1671 m)