I can't answer you question directly, but here are a few clues:
The Daily Eugene (Oregon) Guard, for Saturday, January 18, 1896, page 4, said: "DIED. -- At the Oregon State Insane Asylum at Salem, January 17, 1896, Elias Briggs, an inmate. Deceased formerly resided in Springfield, this county, and was sent to the asylum from that place about a year ago.He had lived at Springfield since the foundation of that town, and was a brother of Isaac Briggs, deceased, who dug the Springfield mill race. Deceased leaves two sons, Ed Briggs, of Springfield, and another son whose whereabouts are unknown.The remains were interred at Salem."
There was an article in the Eugene Register-Guard on 5 June 2004, that said that an employee of the city of Springfield, Paula Guthrie, was collecting information about Briggs in hopes of producing a biography.Her email address then was email@example.com her phone number was (541)484-6010. I don't know if that contact information is still valid.