REMOVE

1. sky
2. pipes (conduits)
3. roads
4. automobiles
5. hills
6. buildings (structures)

WHAT

1. Visual Works (hierarchy n … (1)
2. exterior views (1)
3. fences (1)

More 

WHERE

1. Alberta, Canada (1)

WHO

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

WHEN

1. 1920 (1)
2. 1945 (1)
3. between circa 1929 and ci … (1)