REMOVE

1. sky
2. hills
3. paths
4. soil
5. machinery
6. barriers

WHAT

1. Visual Works (hierarchy n … (2)
2. benches (furniture) (2)
3. black-and-white film (2)
4. branches (plant component … (2)
5. buildings (structures) (2)

More 

WHERE

1. Westminster, Maryland (2)

WHO

1. Campbell, Sandra L. Still (1)
2. Sandra L. Still Campbell; … (1)

WHEN

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