Hi L, They are an elusive couple. Here's what I found. First I found their marriage info.
Washington C. Gwinn married Juda G. Ford, 8 Oct 1868, Saline Co., MO. Source: Missouri Marriage Records 1805-2002.
In 1900 some of their family lived in Woodland, Yolo Co., CA. Washington C. Gwinn, b. MO Feb 1846, marr 31 yrs, night watchman city. Judith G., wife, b. MO March 1850, had given birth to six children but only five alive in 1900. May L., b. MO Dec 1869, single, tailor. Fannie T., b. MO Sept. 1883.
In 1910 they were living in Gilroy, Santa Clara Co., CA. Washington C. Gwinn, b. MO, 64, marr 41 yrs, fruit farmer. Judith, b. MO, 60, had given birth to five children who were alive in 1910. Francis, b. MO, 26, single.
I did find a Laure May Gwinn Page b. 6 Dec 1869, MO who died 16 Sept. 1957, Sacramento Co. Father=Gwinn. Source: California Death Index 1940-97, Ancestry.
In 1920 she and her family were living in Sacramento, Sacramento Co but neither one of her parents were living with them.
Births, marriages and deaths in California are recorded in the Clerk-Recorder's office. I'd check the office in each county to find Washington and Judith's death info. Contact info for Yolo County is at kindredtrails.com/CA_Yolo.html.
Another point is that a city of West Sacramento is located in Yolo Co. Don't know if that makes a difference or not. Successful Searching!