Hi Arlynda, I found the Barnes Family Tree on Ancestry which contains Eli Harper and Sarah Helen Ellsworth. It says that they were married 28 Dec 1887.
However, Eli in 1900 was living in Republic, Ferry Co., WA as a single man.
I looked in Ancestry and FamilySearch for the actual marriage date but didn't find it.
The Gilliam County Records Inventory contains marriage records for their county at the Oregon State Archives. Go to arcweb.sos.state.or.us/county/cpgilliam/marr.html for a listing of the marriage dates they have.
Click on the "Contact Archives" tab on the left-hand side to find out how to ask the Archives to look for a specific record.
If that doesn't work out, you can contact the Gilliam County, Oregon HIstorical Society, rootsweb.com/~orgillia/HistoricalSociety.htm who does research for a reasonable fee. Successful Searching!