Silica Road

Interstate 90 crosses the Columbia River at Vantage. Heading east the highway climbs up out of the deep river valley to the tops of the basalt cliffs and skirts the northwest end of the Frenchman Hills and enters the Quincy Basin.

Silica Road is a familiar exit for Gorge concert goers. The concert venue is located at an ice age spill way where flood water from ice age floods spilled out of the Quincy Basin into the Columbia River gorge. 

Silica road passes through an area of surface mining. The mines mine silica from old lake beds that formed between lava flows of the Columbia River Basalts.

White area on horizon is one of the mines

The silica is diatomaceous material. That is the silica is the accumulation of diatom shells on the lake beds. The lakes must have received very little sediment and thus the diatoms were the primary sediment accumulation in the lake bed. Diatomaceous material has lots of uses from high quality water filters to natural pesticides (the rough mirco glass structure of the silica is hard on bugs).

The ongoing mine activity is located both south and north of the Interstate.

Mines north of Interstate 90. Silica Road passes through this area on the way to the Gorge.

Mines south of Interstate 90.

The mine reclamation requirements are overseen by the Washington State Department of Natural Resources. The mines to the south of the Interstate are in areas with preexisting soil cover and have been reclaimed back to agricultural use. I recall one mine received an award for the reclamation work completed.