Christi,
Sorry I haven't more for you but a few traces of Olsons in the county besides your great grandparents:
county burials, OHLSON, Henry,17 Jul 1920, County Cemetery;
OLSEN, Elak, 21 Apr 1905, Chanate Road Cemetery;
OLSON, Thevorld, 26 Jan 1905, 20 Apr 1905, Chanate Road Cemetery;
OLSON, Jacob, 01 Feb 1905, 19 Apr 1905, Chanate Road Cemetery;
OLSON, Martin, 26 Nov 1926, County Cemetery;
Pleasant Hill burials (rural cemetery near Sebastopol),
single stone, OLSON,Christina,1841-1935; next,
double headstone, OLSON, Gustav A.,1874-1954 & OLSON, Sophie, J.,1873-1952; close by is one unreadable stone, one unreadable wooden marker, and graves for KNEALE & WRIGHT.
I hope this gives you some clues!
Carol Haywood
The GENIE of Genealogy