Explanation:
In dwindling twilight
at an August day's end,
these broad dark bands appeared in the sky for a moment, seen from
Robert
Smithson's Spiral Jetty on
the eastern shore of Utah's
Great Salt Lake.
Outlined by rays of sunlight known as
crepuscular
rays, they are actually shadows cast by
clouds near the distant western horizon, the setting Sun having
disappeared from direct view behind them.
The cloud shadows are parallel, but seem to converge in the distance
because
of perspective.
Coiled in the salt-encrusted lake surface,
Smithson's most famous earthwork
provides a dramatic contrast to the converging lines.
The Spiral Jetty was constructed in 1970, when the water level was
unusually low and was completely submerged in a few years
as the level rose.
Now just above water again, it has spent much
of its existence submerged in
the briny lake.
