REMOVE

1. sky
2. houses
3. rock
4. roads
5. barriers
6. combines

WHAT

1. Visual Works (hierarchy n … (1)
2. arcades (structural assem … (1)
3. benches (furniture) (1)
4. buildings (structures) (1)
5. campuses (1)

More 

WHERE

1. San Francisco, California (1)

WHO

1. Clyfford Still; Still, Cl … (1)
2. Still, Clyfford (1)

WHEN

1. 1946 (1)
2. 1950 (1)
3. between 1946 - 1950 (1)