Betty:
I finally realized that I know you! My sister is Ann Wylie at Hope and my mother is the Mary Cox that you mentioned as having helped you with Hildebrand genealogy info in years past.

I'm afraid I don't have any answers to your questions about the two Mitchells, and I don't know of any Hildebrands that have done more research on Nevada County Hildebrands than Mother. Sounds like from your description of directions traveled from Prescott north and then east, that the country church they went to could have been at the community of Boughton. The cemetery for that community is Piney Grove. If you contact me directly, I can get you in touch with a fellow that researches all the old newspapers of Nevada County and also the cemeteries, and perhaps he's located an obit for Martin Mitchell and/or Hattie or John Mitchell.
Cathy