I think you need to contact Random Acts Genealogical Kindness. Go to raogk.org/, read guidelines, choose California, choose Humboldt Co. and choose one volunteer who does cemetery work.
There is also a Redwood Genealogical Society in Humboldt Co. who also might have info. You can find their contact info at cagenweb.com/humboldt/resource.html .
Also a Humboldt County Historical Society, humboldthistory.org/fees.htm . Successful Searching!