High on a Hill: Emerald Sidewalks
In winter and spring, San Francisco's sidewalks can become green, but not with envy. Depending on the mineral content of the concrete and nearby pavement and even buildings, sidewalks can be a breeding ground for algae and moss. During rainy months, long stretches of sidewalk are rife with the stuff. This phenomenon often occurs on bricks with high iron content and around brick buildings. Nobody seems too troubled by the presence of Emerald Sidewalks. To some, in fact, the are a familiar detail and a reminder of the changing seasons in the heart of the City.

Detail I
Detail II

Copyright 2002 Hank Donat
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