Both PRIMARY and SECONDARY sources are used when researching the history of people, places, and events. They are original records created at the time of the historical event produced by participants or eyewitnesses. They may also be created after the event in the form of memoirs, autobiographies, and oral histories. They include documents such as letters, diaries, court records, interviews, original art work, photographs, treaties, surveys, and research data, etc.
These primary sources may be published and available in multiple copies. For example; this library has a copy of the New Helvetia diary; a record of events kept by John A. Sutter and his clerks at New Helvetia, California from September 9, 1845, to May 25, 1848, in Special Collections and University Archives. It was published in 1939, not 1848, but is still considered a primary resource as it is a facsimile copy in the handwriting of John Sutter and others. For original gold rush diaries you probably would need to go to the California Room at the California State Library downtown or to the California Historical Society in San Francisco.
Other examples of published primary sources are government documents like the census, public records, or a published interview.
SECONDARY sources are broadly defined as works that explain, interpret, or analyze historical events, lives, or places. Often, secondary sources are based on, or are produced using, primary sources.
An article in Political Science Quarterly, "Woodrow Wilson, Alice Paul, and the Woman Suffrage Movement", (Graham, 1983) would be a secondary source. However, the author's research was based on primary sources such as the Woodrow Wilson Papers and interviews with Alice Paul. Students are most familiar with secondary or tertiary sources such as textbooks, encyclopedias, and articles.
Use OneSearch, the CSUS Library catalog, to locate all primary sources (books and other monographs, journals, videos, government documents, etc.) in the Library. You'll often find them under your subject heading with the sub heading "-Sources" such as
Sacramento (Calif.) -- History -- Sources
Many primary sources are now available online as part of digitization projects at museums, libraries and archives. If you do a web search by your topic with the words "Manuscript" "photograph" or "diary" you are likely to find primary documents.
Images and photographs are also primary sources. This library has historic photos in its Special Collections and University Archives. Collections are available to researchers by appointment only. The Center for Sacramento History now has the Harry Sweet Collection of local television news clips covering the Central Valley from 1967 to and 1981.