REMOVE

1. towers (building divisions)
2. campuses
3. sky
4. 1970

WHAT

1. Visual Works (hierarchy n … (1)
2. branches (plant component … (1)
3. buildings (structures) (1)
4. colleges (buildings) (1)

More 

WHERE

1. San Francisco, California (1)

WHO

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

WHEN

1. ca. 1970 (1)