From the OVC:
http://public.findlaw.com/traffic-ticket-violation-law/state-traffic-law/oregon-traffic-law.html
815.233 OREGON VEHICLE CODE
(Mirrors)
815.235 Operation without rearview
mirror; exemptions; penalty. (1) A person
commits the offense of operation without a
rearview mirror if the person does any of the
following:
(a) Drives or moves on any highway any
motor vehicle that is not equipped with a
rearview mirror or device that meets the re-
quirements under this section.
(b) Owns a motor vehicle and causes or
knowingly permits the vehicle to be driven
or moved on any highway when the vehicle
is not equipped with a rearview mirror or
device that meets the requirements under
thissection.
(2) A rearview mirror or device only
meets the requirements of this section if it
enables the driver of the vehicle to have
such a clear and unobstructed view of the
rear at all times and under all conditions of
load as will enable the driver to see any
other vehicle approaching from not less than
200 feet in the rear on an unobstructed road.
(3) This section does not apply to the
followingvehicles:
(a) Vehicles of special interest that are
registered under ORS 805.020 and that were
not equipped with rearview mirrors when
originallymanufactured.
(b) Road machinery, road rollers or farm
tractors.
(c) Antique motor vehicles that are reg-
istered under ORS 805.010 and that were not
equipped with rearview mirrors when ori-
ginallymanufactured.
(4) The offense described in this section,
operation without a rearview mirror, is a
Class C traffic violation. [1983c.338 §493; 1985
c.69§3]