REMOVE

1. sidewalks
2. automobiles
3. rock
4. freight cars
5. buildings (structures)
6. railings (balustrades)

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. black-and-white film (1)
4. bushes (1)

More 

WHERE

1. Westminster, Maryland (1)

WHEN

1. 1961 (1)
2. after 1961 (1)