REMOVE

1. shadows
2. machinery
3. sky
4. horizon line

WHAT

1. Visual Works (hierarchy n … (1)
2. black-and-white film (1)
3. farms (1)
4. fences (1)
5. fields (land) (1)

More 

WHO

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

WHEN

1. 1920 (1)
2. 1940 (1)
3. between 1920 - 1940 (1)