In 2008 I visited the Bay Area with a six-foot level having a calibrated slope-measuring instrument. For each of the results below, I made 5 measurements on each of two separate days and averaged the results. I was careful to measure so that local, short-period irregularities did not skew the numbers.

In the following list, the first street in parentheses is at the top of the hill; the other is at the bottom. The numbers are percent grade [i.e., the tangent of the angle of the street with the horizontal]:

San Francisco (all streets one-way down):

22nd Street (Vicksburg to Church): 31.7%
Filbert Street (Hyde to Leavenworth): 31.3%
Kearney Street (Vallejo to Broadway): 30.3 %

Berkeley (Marin is a two-way street):

Marin Avenue (Hilldale to Euclid): 25.9%
Marin Avenue (Grizzly Peak Blvd to Keeler): 25.0%
Marin Avenue (Keeler to Hilldale): 24.4%

As a footnote, in Laguna Beach, California, the block of 3rd Street between Park and Mermaid has a 30.3% grade. Amazingly, it is a two-way street!