REMOVE

1. freight cars
2. railroads
3. plants
4. paths
5. buildings (structures)
6. black-and-white film

WHAT

1. Visual Works (hierarchy n … (1)
2. bushes (1)
3. exterior views (1)

More 

WHERE

1. Killam, Alberta, Canada (1)

WHO

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

WHEN

1. 1920 (1)
2. 1940 (1)
3. between 1920 - 1940 (1)