I recently learned that the Bay Bridge onramp at Harrison and Essex, which currently looks like:

… used to look like:

It turns out this part of SoMa was originally a well-to-do residential area, until Rincon Hill was demolished in order to make 2nd Street less steep. The upper right-hand corner of this photograph shows 2nd Street passing over Rincon Hill, before the so-called 2nd Street Cut:

… compared to after the cut:

Flattening 2nd Street made the Rincon Hill area more accessible to working folks, which apparently led to the fancy folks moving to Nob Hill. The resulting socioeconomic topography of the city (seems to) persist into the present day.

References

FoundSF: 2nd Street Cut, Rincon Hill, South Park

Wikipedia: 1, 2