REMOVE

1. machinery
2. scaffolds
3. paths
4. trees
5. banks (landforms)
6. 1936

WHAT

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

More 

WHERE

1. Grand Coulee, Washington (1)

WHO

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

WHEN

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