The Portolá Festival of 10/19-23/1909 marked the 140th anniversary of Gaspar de Portolá's discovery of San Francisco Bay. The first major San Francisco event after the 1906 earthquake and fire, it celebrated the city's rapid recovery and demonstrated San Francisco's ability to host the planned 1915 Panama-Pacific International Exposition. cardboardamerica.org describes the genesis of the Festival in detail and The Portola Festival by Harry K. Charles Jr. gives an overview of Portolá Festival postcards. Almost all of the postally used cards on this page are postmarked just before or during the Festival.
Each of these cards was postmarked in the three weeks preceding the Festival.
San Francisco lithographers Britton & Rey produced a set of eight "official" Festival postcards (9008-9015). 9010, 9012, and 9015 superimpose the same group of revelers on San Francisco views from other cards. The backs of 9009, 9010, and 9011 give data about the city and the fire; the backs of 9008, 9012, and 9015 provide information about Portolá.
These cards show the Festival parade on Market Street on 10/21/1909.
Steve's SF postcard pages: