I need some advice on where to start.  My recently found 1/2 uncle told me that there is a 1/2 sister out there.  His father had an affair when my 1/2 uncle was in high school.  All he remembers is that the woman was a Native American and the child was a girl.  He had hoped that when he went through his parents things after they passed he'd find something referring to this birth. There wasn't anything. There were several things about my dad, who was from the bio father's first marriage.  The brothers have gotten together and are happy to have finally met after 68 years.

The girl would have been born in Contra Costa County, California somewhere between 1957-1959.  That, and that her mother was Native American, is all I know.  And they want me to find her! 

I've started searching the Contra Costa County birth indexes on Ancestry, but without a name.... let's just say that I'm on page 105 and haven't reached the "C"'s yet.  I am looking for girls whose birth mother's maiden name is the same as the child.  There are quite a few.  Did she put "Hughes" down as the father's last name? Did she marry before the child was born so a different father's name is on the birth certificate?  Did the child get put up for adoption?  So many things to look for.  It's worse than the needle in the haystack. 

I would appreciate any advice you could give on how to procede with this task.