The Contra Costa County Historical Society collection contains print materials from the 1870s through the 1900s. The majority of the collection consists of accessors maps, and include subjects and topics such as Contra Costa land owners, plat maps and more.
The Petaluma Historic Library and Museum collection contains texts and audiovisual material (moving images, audio) and texts from the 1920s to 2010s. A majority of the collection consists of oral histories, interviews, and home movies concerning Petaluma Chicken Ranches, genealogy, the Argus Courier Newspaper, the Bojorques family and more. Other material includes texts such as oral transcripts and maps about the history of ranchos.