The Los Angeles Times reports ( http://lat.ms/XbDZeO) Casey Tschida was taken into custody Saturday at his mother's home in Happy Valley, near Portland.
San Diego homicide investigators are arranging for him to be returned to Southern California.
Sheriff's investigators say Tschida drove to Oregon after the Thursday morning shooting in the Lemon Grove area.
Authorities say 30-year-old Jennifer Krajnak was shot in the head while walking home from a bar, where she and Tschida had been.
Deputies on patrol found her along the side of a road. She was pronounced dead at a hospital.
Detectives have no motive.
Information from: Los Angeles Times, http://www.latimes.com