Here are some resources outside of USC Libraries that feature digital primary sources:
Online Archive of California: The Online Archive of California (OAC) provides free public access to detailed descriptions of primary resource collections maintained by more than 200 contributing institutions including libraries, special collections, archives, historical societies, and museums throughout California and collections maintained by the 10 University of California (UC) campuses.
Calisphere: Calisphere provides free access to unique and historically important artifacts for research, teaching, and curious exploration. Discover over two million photographs, documents, letters, artwork, diaries, oral histories, films, advertisements, musical recordings, and more.
The Freedom Archives: The Freedom Archives contains over 12,000 hours of audio and video recordings which date from the late-1960s to the mid-90s and chronicle the progressive history of the Bay Area, the United States, and international movements.
Digital Public Library of America (DPLA): DPLA works with a network of partners to make millions of materials from libraries, archives, museums, and other cultural institutions across the country available to all in a one-stop discovery experience.