REMOVE

1. rock
2. trees
3. sky
4. barriers
5. hills
6. mountains
7. machinery
8. buildings (structures)

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. beards (1)
4. benches (furniture) (1)
5. bushes (1)

More 

WHERE

1. Westminster, Maryland (1)

WHEN

1. 1970 (1)
2. 1975 (1)
3. between 1970 - 1975 (1)