Use the library catalog. Books may only have broad subject headings, so if you are seeking information on a more specific topic you may have to broaden your search. For instance you might not find anything under the name of an individual who might be covered in a collective biography try a heading such as "Butte County (Calif.) - Biography" or an historical work under a heading like "Chico (Calif.) -- History."
These can be difficult to find since relatively few articles about this area are listed in major online journal databases, particularly for historical coverage. More recent articles may be available in sources such as LexisNexis or Academic Search, but again you may have to broaden your subject.
These are more plentiful and easier to find. Go to "News Sources" and select an online newspaper such as the Chico Enterprise-Record, Chico News & Review, or The Orion. These all have an archival search capability. There is also an online index to two local newspapers, the Orion and the News and Review.
The latest issues of newspapers and most back runs are found in the Media & Microforms area. There is a card file for environmental topics in the Enterprise-Record and some other local papers dating from 1972-1996 on the second floor of the library. Otherwise, just scan the newspapers on microfilm by date. Warning: this can be very time-consuming.
These collections are located in Special Collections on the third floor. Special Collections is open limited hours, typically 10-5 on weekdays. Check the schedule.
Special Collections has several digital collections and other services. These include a substantial collection of historic photographs, University Archives, and a Digital Geographic Data Collection.
Since "Chico" is also a word and a common first name, be sure to qualify any web searches to include the entire phrase "Chico California." Try Google Advanced Search.
Chico and Butte County information can be found on the City of Chico and Butte County Government websites.