REMOVE

1. boys
2. railroads
3. trees
4. windows
5. rubbish
6. rock
7. roads

WHAT

1. automobiles (1)
2. banks (landforms) (1)
3. black-and-white film (1)
4. branches (plant component … (1)
5. brick (clay product) (1)
6. buildings (structures) (1)
7. bushes (1)
8. children (1)
9. exterior views (1)
10. fields (land) (1)
11. forests (plant communitie … (1)
12. freight cars (1)
13. garages (1)
14. hills (1)
15. landscapes (representatio … (1)
16. men (male humans) (1)
17. plants (1)
18. rails (transit system ele … (1)
19. signs (declatory or adver … (1)
20. sky (1)
21. soil (1)
22. trains (vehicle groupings … (1)
23. utility poles (1)
24. Visual Works (hierarchy n … (1)
25. wheels (components) (1)
26. workers (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)