Hi Arlynda, I found a family tree on Ancestry which included your John Harper. I asked the author to contact you.
Cemeteries located in Eugene can be found at the following web sites:
USGenWeb Tombstones, usgwtombstones.org/oregon/lane.htm I Dream of Genealogy, idreamof.com/cemetery/or.html Interment.net, interment.net/us/or/lane.htm
You can search through their listings and see if you can find your John Harper.
I don't want to sound negative, but you might not find him if he was indigent when he died or a family member didn't have the money to pay for his funeral which is generally the case when someone is buried in 'Potter's Field'.
Also cemetery records over the years can be abysmal. People are interred with a wooden cross or metal marker which deteriorates over the years and the cemetery doesn't replace it.
You can also contact the Oregon Genealogical Society and Research Library, rootsweb.ancestry.com/~orlncogs/ogsinfo.htm and see what they have. SOMETIMES the local genealogy society will have more information than what is on-line. Successful Searching!