She was born Marilyn Bigger on 26 July 1952. She married Fernando Arraztoa 23 June 1973 in California, which ties in with the NAMUS link to her engagement announcement. Oddly, they then divorced in August 1973. Whilst this may just be a case of finding they were incompatible I do wonder, given the speed, if there was a green card issue here as the husband was a Spanish national. Marilyn remarried in 1975 to Harry D Waltz, who still appears to be living in Bakersfield. I cannot find any definitive confirmation whether they were still together when she went missing but there does not seem to be a divorce record. However, there is a 1978 listing in the city directory for Bakersfield which has Don and Marilyn Waltz listed and it seems Harry Waltz used his second name, Don, as his father was also Harry. So it seems likely they remained married and together. This information comes from Ancestry.
It appears that Marilyn must have been declared dead at some point before 1986, or Harry Waltz must have secured a divorce, as Ancestry has a marriage record for Harry Don Waltz Jr to Joyce Ann Jones in Nevada in October 1985. I assume this is the same Harry Waltz.
Various sources report Marilyn as having a caesarean scar, indicating a child or children. I am pretty sure this is Leslie Waltz, a daughter born 21 June 1976. The Ancestry record of her birth shows the mothers maiden name as Bigger. She is also shown as related to Harry D Waltz in various places such as Radaris so this all ties in. She also still seems to be in Bakersfield under her married name of Leslie I Smith.
All of this just raises one obvious question; given the family and child why is there so little information out there. Are they not looking or do they know what happened (which may not be sinister, she may just have chosen to walk away)?