During the gold rush in 1849 a couple of doctors and an interesting character, a surveyor/glass blower/instrument maker, began taking rainfall measurements in San Francisco. They sold this data to local newspapers and an almanac. In 1871 the army signal service began official recordings.
In spite of the fact that the US GOVERNMENT has recorded the precip data since 1871 the data does not appear to be available from the NCDC. They refer you to the National Archives, of which only a small portion has been scanned.
While cruising the NCDC site I did find an extremely cool ENSO index based on rainfall records from northern China from 1470. It seems one can get index from pre-columbian (yes, that is 22 years before Columbus sailed the ocean blue) rainfall data from China but nothing from late ninteenth century San Francisco!!