I see this is your first posting using this user name. When you post it is VERY important to fully identify the person(s) you seek. In this case, Althea's date of birth would have been very helpful. Also very helpful was your knowledge she married Fred Dupont. It was only after quite a search that I found, not the family tree shown below, but others that listed Althea and Fred. There isn't that much information about either one.
You will have to first attempt to obtain her obituary in San Francisco from 1972. Also the obituary of Fred Dupont. I don't know if they were still married at the time of her death, or the situation. You probably do. Your grandmother Effie and Grant Seavy either divorced, or he had died before 1943 when she was found married to a Collins.
To do this genealogy, your FIRST step is to talk to any living family member about them. Document all verbal information. Then identify any old family pictures from albums, personal records, etc. that is still in the family. I don't know if your father was David Dupont, or his sister was your mother, but begin within this small network of family. THEN obtain obituaries of the next level back.
I found your family tree:http://trees.ancestry.com/tree/4694897/person/-1563489700?ss...
It doesn't help much for this search. Effie is shown as having one brother, Homer, born 1873, and four sisters. Parents James Milligan, mother Sarah McConough.
--California Death Index, Effie Collins, born 29 Jan 1880 in Ohio, mother's maiden name "McConnel" father's surname "Milligan," died on 19 Oct 1943 in Orange County. So it appears Grant Seavy died, or there was a divorce.
You had posted in the past that a Fred James Dupont, born in Oakland about 7-10-1902, his mother born in Portugal, a sister Dolores. He married Althea L. Seavy.
The 1920 Census for Oakland, Alameda County, CA
Mary Dupont, age 52, born in Portugal, immigrated 1857, Alien(not naturalized), housework/private homes, married
Fred, son, age 17, born in California, Rancher/ranch
Delores, age 5, born in CA.
California Death Index:
--Fred James Dupont, born 10 July 1902 in CA, died 9 May 1981 in Sonoma County, CA, mother's maiden name "Freitas."
--Althea L. Dupont, died 23 Dec 1972 in San Francisco County, CA, SSN: 561-80-7063. This record did not identify her date of birth. An original copy of her own application for her SSN could be obtained from the Social Security Administration. It would show/prove the identity of her parents.
A family tree ownedby "Starr63" identified Althea had a son, David Lawrence Dupont; and, a daughter, "living DuPont."
California Birth Index:
Mary R. Seavey, born 10 Sep 1906, mother's maiden: "Milligan."
Seavey, born 27 April 1918, Orange County, mother's maiden: "Milligan." (This "might" be the birth of Althea, but I found no information as to her birth).
Theodore J. Seavy, born 30 Nov 1904, died 8 March 1969 in Orange Co. His wife, Lillian Ione Fisher, died 12 Feb 1990 in Inyo County, CA. They had a son and a daughter. This information is from a family tree posted by a Charles McClellan, perhaps a cousin? http://trees.ancestry.com/tree/922936/person/-265634716
Informant Lilian Ione Seavy
The East Line Street Cemetery is also known as the "Oddfellows" and "Masonic" Cemeteries. It is located in Bishop, Inyo County, CA.