Cascade Mountain, US Highway 12

Initial situation

US Highway 12 is the Southern most pass that crosses the Cascade Mountain in the state of Washington, USA.  Numerous slopes near White Pass are active rockfall areas.  They have been mitigated over the decades with many solutions including numerous draped mesh systems composed of traditional cable nets.  One such antiquated cable net drape at MP 152 was draped across a rockfall chute and in 2017 was destroyed by severe rock and snow slides.  The Washington Department of Transportation decided to update the system with the stronger and improved Rolled Cable Nets (S4-250).

Geology

White Pass Scenic Byway and was featured in Newell Campbell’s geologic road guide (1975) (Fig. H-1). The byway passes through one of the most scenic and geologically interesting areas in Washington. There are tens of volcanic centers that range in age from earliest Miocene to Pleistocene. Late Paleozoic/Mesozoic sedimentary rocks and metamorphic rocks, glacial deposits, and large active landslides are also exposed along the way. The Russell Ranch Formation is exposed near MP 148 along US 12. The Russell Ranch unit includes marine sedimentary and volcanic rocks that are at least in part of Late Jurassic and Early Cretaceous age (~145–130 Ma).  Numerous Quarternary landslide and talus Deposits are also 

From INFORMATION CIRCULAR 107 (Pringle, et al.)