Vital Search California Death index 1905 to 1929 has a Gladys Allen, spouse initals D.C., age 18, died in 54(Tulare County) d. 11/28/1928. Certificate # 60473. The age 18 makes her birth year abt 1910. Here is the link to look yourself: http://www.vitalsearch-ca.com/http://www.vitalsearch-ca.com/guestpass: vitalguest, password: enjoy
Looking at the the California Birth Index I find your grandfather's birth Nov. 27, 1928 in Tulare County mother's nee Vaughn. I also find a Donald Robert Allen b. 1926 mother nee Vaughn b. Santa Cruz County.
1930 I find your grandfather living as a boarder in the household of an Eva Allen in Fresno, Fresno County CA. I find a Daniel C. Allen (D.C.) with a second wife Dosia and son Donald living in Dinuba, Tulare County, CA.
Looking at the 1920 Census I find Daniel C. Allen living with parents in Dinuba, Tulare Co. CA. I find only one Gladys Vaughn age 10 (b. abt 1910) living in Hanford, Kings County, CA, parents Jesse N. Vaughn and according to an online family tree of oldest brother Basil C. Vaughn, mother Caroline Hicks. This Vaughn family has 9 children including including Gladys child # 8.
Looking back at the CA Birth Index there is a Gladys G. Vaughn b. July 4, 1909 in Kings County mother's maiden name Hicks. In 1910 census the Gladys's age is 10 months in May 1910, in 2 months is July so I am pretty sure this is your grandfather's mother.
She might be buried in Tulare county, the Smith Mountain cemetery outside Dinuba, or she could be buried with Vaughn relatives in a Kings County Cemetery or Fresno, Fresno County as that is where Jesse and Caroline are living in 1930 census.
Jesse Newton Vaughn and Caroline Vaughn both are listed in the California Death Index, they died in Alameda County, he in Sept 1943 and she in Nov 1957. Daniel C Allen d. Jul 1984 in Tulare County also listed. You can view the names at Vital Search 1940 to 2000 or the one at Rootsweb 1940 to 1997: http://vitals.rootsweb.ancestry.com/ca/death/search.cgihttp://vitals.rootsweb.ancestry.com/ca/death/search.cgi
The online family tree for Jesse N. Vaughn can be seen by going to www.rootsweb.com and seaching his name, 2 results in WorldConnect, spouse Caroline Hicks.
Good Luck and please verify as this is my best guess looking at records online.