[1] Born in Walpole, Massachusetts, Gillis served as a history instructor at Butte College (1981–1985) and, for twenty-five years, as a lecturer at California State University, Chico.
As part of his research for the Bidwell book, Gillis undertook an exploratory backpacking trip during which he and his wife located and retraced the probable route taken by the Bartleson-Bidwell Party during its famous trek across the Sierra Nevada in 1841.
Gillis later published an account of the trip, along with his findings, in an article that appeared in the Winter 1998–99 issue of the Overland Journal.
Gillis was also a member of the Butte County Historical Society and the Association for Northern California Records and Research, serving as ANCRR's president from 1994 to 1998.
[5][6] Gillis died April 7 at Stanford University Medical Center after a 10-month battle with a rare liver disease called primary sclerosing cholangitis.