There are several ways to obtain the naturalization information. Ancestry.com has the images in their database. Name: Chg Fred Nelson [Erick Alfred Nelson] State: Oregon Locality, Court: Judicial District of Oregon, U.S. District Court
You can order them from the National Archives (NARA): National Archives and Records Administration (NARA); Washington, D.C.;Naturalization Indexes complied by the Court Clerks at the U.S. Circuit and District Courts of the the Judicial District of Oregon, 1859-1956; Microfilm Serial: M1242; Microfilm Roll: 3.
and from the Oregon State Historical records: Oregon State Archives 800 Summer St NE Salem, OR 97310 503-373-0701 ext. 1 Fax: 503-378-4118 firstname.lastname@example.org