REMOVE

1. sky
2. rubbish
3. hats
4. boys
5. roads
6. hills

WHAT

1. banks (landforms) (1)
2. black-and-white film (1)
3. bushes (1)
4. coats (garments) (1)
5. freight cars (1)
6. ladders (1)
7. men (male humans) (1)
8. plants (1)
9. railroads (1)
10. rails (transit system ele … (1)
11. soil (1)
12. trains (vehicle groupings … (1)
13. trees (1)
14. utility poles (1)
15. Visual Works (hierarchy n … (1)
16. wheels (components) (1)
17. workers (1)
18. wrecks (sites) (1)

WHERE

1. New Windsor, Maryland (1)

WHO

1. Campbell, Sandra L. Still (1)
2. Clyfford Still; Still, Cl … (1)
3. Sandra L. Still Campbell; … (1)
4. Still, Clyfford (1)

More 

WHEN

1. 1969 (1)