Snohomish Variant
silt loam, thick surface variant

Mapping Symbol: Sr

The Snohomish series, thick surface variant, consists of poorly-drained soils that formed in alluvial deposits of diatomaceous materials on the flood plain of the Sammamish Valley. Slopes are 0 to 2%, annual precipitation is 45 to 50 inches, and the frost-free season ranges from 150 to 200 days. Elevation ranges from 0 to 40 feet.

Typical Profile:
Depth from Surface:
0 to 20 Inches: Very dark brown silt loam 
20 to 60 Inches: Black muck

Permeability: Moderate 

Rooting Depth: 60 inches + if drained

Depth to Seasonal High Water Table: 2 to 3 feet

Available Water Holding Capacity: High

Runoff Potential: Very slow 

Erosion and Slippage Hazard: Slight

Stream Overflow Hazard: Occasional

Use and Management: Primary uses are for hay, pasture, and row crops. Pasture forage yields are 3.0 tons/acre/year if undrained and 6.0 tons/acre/year if drained. Douglas-fir, Western Red Cedar, Western Hemlock, Red Alder, Willow, and Sitka Spruce are important tree species. These soils have severe limitations on equipment use for site preparation and timber harvest, seedling mortality, plant competition, and windthrow hazard for forestry use.These soils have severe limitations on recreational and engineering uses due to their seasonal high water table, flood hazard, organic materials, and low shear strength.

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