I'm not from California. I grew up in Washington, moved to Ashland after I finished my bachelors, and moved to Portland a year and a half ago. A significant constant between the Seattle area, the Rogue Valley, and the Portland area is that, more often than not, people who can't be bothered to learn the rules of the road accuse "Californians" of being the bad drivers.
Driving 20 MPH under the speed limit on the freeway is against the law:
811.100 Violation of basic speed rule; penalty. (1) A person commits the offense of violating the basic speed rule if the person drives a vehicle upon a highway at a speed greater than is reasonable and prudent, having due regard to all of the following:
(a) The traffic.
(b) The surface and width of the highway.
(c) The hazard at intersections.
(d) Weather.
(e) Visibility.
(f) Any other conditions then existing.
(2) The following apply to the offense described in this section:
(a) The offense is as applicable on an alley as on any other highway.
(b) Speeds that are prima facie evidence of violation of this section are established by ORS 811.105.
(c) This section and ORS 811.105 establish limitation on speeds that are in addition to speed limits established in ORS 811.111.
(3) Except as provided in subsection (4) of this section, violation of the basic speed rule by exceeding a designated speed posted under ORS 810.180 is punishable as provided in ORS 811.109.
(4) The offense described in this section, violating the basic speed rule, is a Class B traffic violation if the person drives a vehicle upon a highway at a speed that is not reasonable and prudent under the circumstances described in subsection (1) of this section even though the speed is lower than the appropriate speed specified in ORS 811.105 as prima facie evidence of violation of the basic speed rule. (1983 c.338 §563; 1987 c.887 §9; 1989 c.592 §4; 1991 c.728 §5; 1999 c.1051 §229; 2003 c.819 §5)
811.105 Speeds that are evidence of basic rule violation. (1) Any speed in excess of a designated speed posted by authority granted under ORS 810.180 is prima facie evidence of violation of the basic speed rule under ORS 811.100.
(2) If no designated speed is posted by authority granted under ORS 810.180, any speed in excess of one of the following speeds is prima facie evidence of violation of the basic speed rule:
(a) Fifteen miles per hour when driving on an alley or a narrow residential roadway.
(b) Twenty miles per hour in a business district.
(c) Twenty-five miles per hour in any public park.
(d) Twenty-five miles per hour on a highway in a residence district if:
(A) The residence district is not located within a city; and
(B) The highway is neither an arterial nor a collector highway.
(e) Fifty-five miles per hour in locations not otherwise described in this section. (1983 c.338 §564; 1985 c.16 §286; 1987 c.887 §10; 1989 c.592 §5; 1995 c.558 §3; 1997 c.404 §5; 1997 c.438 §3; 2003 c.397 §6; 2003 c.819 §6; 2007 c.367 §3)
Someone driving 20 MPH under the speed limit on the freeway is also require to yield to faster traffic. ORS 811.425 reads
811.425 Failure of slower driver to yield to overtaking vehicle; penalty. (1) A person commits the offense of failure of a slower driver to yield to overtaking vehicle if the person is driving a vehicle and the person fails to move the person’s vehicle off the main traveled portion of the highway into an area sufficient for safe turnout when:
(a) The driver of the overtaken vehicle is proceeding at a speed less than a speed established in ORS 811.105 as prima facie evidence of violation of the basic speed rule;
(b) The driver of the overtaking vehicle is proceeding at a speed in conformity with ORS 811.105;
(c) The highway is a two directional, two-lane highway; and
(d) There is no clear lane for passing available to the driver of the overtaking vehicle.
(2) This section does not apply to the driver of a vehicle in a funeral procession.
(3) The offense described in this section, failure of a slower driver to yield to overtaking vehicle, is a Class B traffic violation. (1983 c.338 §640; 1991 c.482 §16; 1995 c.383 §68; 2001 c.104 §307; 2003 c.819 §15)
If they're in the left lane, they're also breaking the whole 'left lane is only for passing' law. ORS 811.295 reads:
811.295 Failure to drive on right; exceptions; penalty. (1) A person commits the offense of failure to drive on the right if the person is operating a vehicle on a roadway of sufficient width and the person does not drive on the right half of the roadway.
(2) A person is not required to drive on the right side of the roadway by this section under any of the following circumstances:
(a) When overtaking and passing another vehicle proceeding in the same direction under the rules governing this movement in ORS 811.410 to 811.425 or 811.808.
(b) When preparing to turn left in an intersection, alley or private road or driveway.
(c) When an obstruction or condition exists making it necessary to drive to the left of the center of the roadway, provided that a driver doing so shall yield the right of way to all vehicles traveling in the proper direction upon the unobstructed portion of the roadway within a distance as to constitute an immediate hazard.
(d) Upon a roadway divided into three marked lanes for traffic under the rules applicable on the roadway under ORS 811.380.
(e) Upon a roadway restricted to one-way traffic.
(3) The offense described in this section, failure to drive on the right, is a Class B traffic violation. (1983 c.338 §615; 1991 c.482 §15)
The left lane is for passing.
ORS 811.315 states:
811.315 Failure of slow driver to drive on right; exceptions; penalty. (1) A person commits the offense of failure of a slow driver to drive on the right if the person is operating a vehicle upon a roadway at less than the normal speed of traffic at the time and place and under the conditions then existing and the person fails to drive:
(a) In the right-hand lane available for traffic; or
(b) As close as practicable to the right-hand curb or edge of the roadway.
(2) This section does not apply under any of the following circumstances:
(a) When overtaking and passing another vehicle proceeding in the same direction under the rules governing passing in ORS 811.410 to 811.425.
(b) When preparing to turn left at an intersection, alley or private road or driveway.
(3) The offense described in this section, failure of slow driver to drive on the right, is a Class B traffic violation. (1983 c.338 §619; 1995 c.383 §57
If you're driving slow to enjoy the scenery, then you're not paying attention to the road. If you want to enjoy the scenery, do the responsible thing and pull over.