I believe his previous service is the Spanish-American War (around 1898). In the 1930 Fed Census the family is living in California > Imperial > Westmoreland > District 51 > 2
*note there are year of birth discrepancies in census and also on his WWI Draft Registration
1930
Gregg, James E. Head age 55 (1875) age at first marriage 42 yrs, born KY, Father France, Mother Oklahoma- he is a mechanic at a garage and Military for him is Sp. the others on the page have WW.
Wife- Belva is 40, age of first marriage 27, she is a chauffeur, school bus, Missouri, Missouri, Kentucky
Son James E., Jr. age 12 born Montana
Daughter Virgina age 10 born Alaska
--------------------------
California, Voter Registrations, 1900-1968
Return to Search Results Imperial County > 1920-1926 > 714
Tammarack Precinct
Mrs. Belva T. Gregg, Housewife, Republican, Brawley, California , Box 1575
James E. Gregg, Rancher, Republican, Brawley, California, Box 1575
Same county, address in California Voter Registration Records in 1928-1932
_____________________________________
James E. Gregg WWI Draft has him born in 1887 but born in Paris, KY so a wide variation on his date of birth.
From what I've read it is harder to research on Spanish American War Veterans, but not entirely impossible. The US Revenue Cutters (before birth of Navy) patrolled the water to protect the Klondike.
This site might help you in researching files of his service in Spanish American War. Since his previous service indicated was in Washington State, I would say he was around that Area possibly in the 1900 census (sure did move alot!)
Have you located their divorce records?
Who was the informant on the Death Certificate - a relative or a nursing home or hospital records person?
When you found his plot in the Cemetery, there should be a burial card of who purchased the plot, many list parents name and other pertinent information.
It's going to take some searching in 1940 as it's apparent they are divorced by this time, and son James is living the relatives Sullivan. But is indicated he lived in 1935 Harve, Montana. These ancestry hints are usually a hint created by others that have found them already and attached to their records. My first inclination would call the cemetery and have them give you the burial card info first, and then find where the divorce took place. It will yield more information as to where he could be possibly living in 1940 California or Montana most likely. Someone kept in touch or knew where to locate him upon Virginia's illness for him to come to see her before she died. As far as why he didn't keep in touch more, I saw the description on your Memorial on Find A Grave, probably this was the reason the family divorced and moved on.
http://www.spanamwar.com/geneaol2.htm