I reviewed your profile and found your family trees. The dana Sullenger tree did not have any additional information that wasn't identified in your post to help a volunteer. (Also, being of the same gov't service, I salute yours).
Your initial posting indicates you are searching the Mihelich family as opposed to finding information about Margaret/Jack and this Barlow family. When you post, post the FULL search data you are attempting to find, post the name (such as Margaret's), their full date/place of birth if you have it, and the parents name if you have it (you did).
There is absolutely nothing in the family history of either Margaret or Jack to indicate they married in Los Angeles County. Jack Barlow was in LA County in 1930...14 years of age. In 1935, he was in Lake Isabella, which is in Kern County. He died in Kern County, per the CA Death Index (but a Death Index based on death certificate [as is the CA DI] does not prove they lived there). From 1930 to 1996 is a LONG TIME for this person to have met and married, even far away from where they had lived (many go to Las Vegas...). He is of the age to have served in WWII and may have been married prior to Margaret, or met her in Arizona during War time military activities, etc...
The 1940 Census: Arizona has been transcribed about 2 percent, Oregon 89 Percent, California 6 percent. BUT, there is no way to determine that these two were even married by 1940 (unless you have that information, based on the children). The children's information may be more inportant than the genealogy research data. If you do not have contact with the children, THEY may be the holder of the information you seek, if you seek the marriage data.
--The 1940 Census of Isabella appears to be in the Enumeration District 3, Judicial Township 1, of Kern County. There are 42 images of that area, I checked the sheets but no Barlow. So, they may not have been there, or were missed, or... ?
I would NOT spend money to check for marriage records in LA County or Kern County, unless you have information that indicates they were there, or a bonifide volunteer comes up with documentation.
At this point, you need to review other information you may already have. Do you know where the children were born and when? If they were born after the 1940 census, then finding "Jack" and Margaret might be more difficult in the 1940 census. Do you have any information about their anniversary year (For example, an obit might identify Jack was married "40 years" when he died, or they were together 42 years). Again, any contact with the children might identify more information.
Now, again at this point, what is your GOAL? To identify the marriage date and place...OR to learn more about Margaret's family?
I'll also message you direct with information about other "help."