Cecilia - Thank you for the data. I would appreciate your looking in the death records for David; and Mary too, if you have the time.
The RootsWeb California Death Index, which only covers 1940 - 1997, has a Robert Jehu Craig b. 1880, d. 12/24/1950 in Sonoma County. It has some other people with MMN Barnes, Father's surname Craig who look likely, but Robert Jehu leaps out. If Robert Jehu is Mary's son, and named after her father, as seems likely, the Mary E. who married Mr. Cofer is a different one, not David's widow.