Edward H. Mitchell (b. 4/27/1867 in San Francisco, d. 10/24/1932 in Palo Alto) was a prolific postcard publisher in San Francisco from the 1890s through 1923. Mitchell was a businessman, not a photographer, so his cards use images from many sources. Mitchell's offices were at 225 Post pre-quake and at 3363 Army (now Cesar Chavez) post-quake.
Mitchell was in the postcard buisiness for decades, and unlike most postcard publishers he frequently reused a stock number, sometimes with an updated image, sometimes with a totally different image. Mitchell Variants, Cliff House from Ocean Beach and Mitchell 30 dups provide examples.
The print quality of Mitchell's later postcards is often poor, unlike his earlier cards.
Online sources:
Steve's SF postcard pages: