Scotia Bluffs is a two-mile stretch of gray sandstone cliffs along the lower Eel River near Rio Dell, where the river turns against the fossil-bearing Rio Dell Formation. Turbulent water carved deep pools below the cliffs, and tributaries cut steep canyons through them. Rising roughly 75 to 500 feet above the old rail line, the bluffs became one of the hardest railroad passages on the lower Eel. Railroads built across the cliff face from 1883 onward were repeatedly damaged by floods and falling sandstone, causing decades of interruptions. A 1953 landslide swept engine 184 into the river and killed three trainmen, underscoring the route's dangers.