The Narrator Tells Us What Hides Behind These Brick Walls.

…Of Course, He Is Contrasting What Is Lost In Comparison To the Wild, Wide Open Montana Mountain Places of This Country He Knows So Well!

…“[It is the little, pathetic attempts at Quality that kill.] The plaster false fireplace in the apartment, shaped and waiting to contain a flame that can never exist. Or the hedge in front of the apartment building with a few square feet of grass behind it. A few square feet of grass, after Montana. If they just left out the hedge and grass it would be all right. Now it serves only to draw attention to what has been lost.” (University of Chicago. Cont. Next.)

Where HSG could find parking on S. Ellis Ave, North of University of Chicago, Chicago, IL. From the Narrator's Chicago apartment building’s experience, he surely knew very well what the tiny strips of grass looked like, and what was inside many of these apartments.
…I experienced the very things described in the ZMM passage above, including the very tiny patches of grass, when I was a student in the old, congested, inner-city apartment areas of Cleveland, OH (1955 – 1968).
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(Photo = 101-0153cz1.4 ...... ZMM Page = 356 ...... WayPt = -034 0590 ft)