REMOVE

1. rubbish
2. trees
3. boys
4. rock
5. buildings (structures)
6. banks (landforms)

WHAT

1. Visual Works (hierarchy n … (1)
2. automobiles (1)
3. black-and-white film (1)

More 

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)