Salem History - click browse tab, select by Geographical Location
JSTOR - strong collection of scholarly articles on historical topics; mostly considered secondary sources. Difficult to refine by topic, but Advanced Search lets you narrow by discipline.
EBOOKS! Since our books are in the new library, and we only bring them over as requested once a day, you might want to try ebooks. Create a free personal account in EBSCO, and you'll be able to download books and read them in the Bluefire Reader app in iTunes or Android store.
Use infomine.ucr.edu as a decent search tool for academic and scholarly websites (avoid the $ pay per view sites)
Search for selected sites using the Google operators. inurl:library site:edu guide [insert relevant terms], e.g., Mexican American