One man is dead and a second in critical condition following a single vehicle rollover crash on westbound Interstate 84 six miles west of Arlington.  The Oregon State Police says 24-year-old Justin Matthew Flowers of Portland died from injuries suffered in the accident, while 23-year-old Hayden Michael Swanson of Portland is in critical but stable condition at Oregon Health Sciences University Hospital in Portland.  The OSP says the accident occurred at about 4:30 Sunday morning.  An investigation indicates the SUV Flowers was driving was westbound on I-84 when it left the roadway for unknown reasons, crashed through the north side guardrail and rolled down a rock embankment, coming to rest approximately 150 feet from the roadway.  Preliminary information indicates the men had not been using their seat belts at the time of the crash and were ejected from the vehicle.  Speed and fatigue are being considered to be contributing factors for the crash.