Thank you very much for taking the trouble to post this information.Jim Gardner also sent me an email.Below is part of my reply to him.
My ggg grandfather Edward Marlow died intestate in Burlington, Des Moines Co, IA in 1852.I have his probate papers, and "Stephen M. Gardiner" shared equally with Edward's other heirs, namely, his then living children and a granddaughter.Stephen's share was signed for by my gg grandfather Henry Bartruff, husband of Edward's daughter Mary Ellen.One of the probate papers states Stephen was in California in August, 1853.A plat of the land of Edward's estate in the probate papers shows the equal division among heirs, and lists him as "S. B. Gardner."I can account for all of the other heirs.What makes the most sense is that Stephen was the son of a deceased daughter of Edward, which accounts for my interest in the parents of the query's Stephen B Gardner.I have no idea where my Stephen went after 1853.
Over time I have compiled quite a bit of information on Edward and his children, but this Stephen eludes me.The only information I really have is the meager mentions in the probate papers.This Stephen B. Gardiner of Curry Co. looked like a pretty good possibility, but your information seems to rule him out.