The Oregon-California Trail Association also known as OCTA, has been dedicated to preserving the Oregon Trail and its history. Be sure and check the site for links to the individual OCTA Chapter Web Sites and visit the OCTA Book Store
Overland Trail by Liz Larson is an excellent site.
The Oregon Trail brought to you by Mike Trinklein and Steve Boettcher, is based on the award winning documentary film which was aired nationally on PBS Stations.
CALIFORNIA:
The CA Pioneer Project offers lists of individuals that settled in California prior to 1880. Be sure and check this site out.
CA GenWeb offers county sources for finding early pioneers to California. Many early emigrants to Oregon moved to California and vice versa.
CA Library Holdings Database provides listings of holdings in the CA library system and their location
IDAHO:
Idaho GenWeb provides county sources for the state of Idaho
WASHINGTON:
Washington GenWeb provides county sources for the state of Washington