REMOVE

1. rivers
2. fences
3. clouds
4. atmospheric perspective
5. Grand Coulee, Washington

WHAT

1. Grand Coulee Dam (dam) (1)
2. Visual Works (hierarchy n … (1)
3. banks (landforms) (1)
4. barriers (1)

More 

WHO

1. Clyfford Still; Still, Cl … (1)
2. Still, Clyfford (1)

WHEN

1. 1936 (1)
2. 1937 (1)
3. ca. 1936 - 1937 (1)