Hate to rain on your parade.
That fs link is forest service roads, so you can run for miles and miles, till the cows come home.
From Wiki.
Oregon Law (ORS 801.258) defines an electric assisted bicycle as an electric motor-driven vehicle equipped with operable pedals, a seat or saddle for the rider, no more than three wheels in contact during travel. In addition, the vehicle must be equipped with an electric motor that is capable of applying a power output of no greater than 1,000 watts, and that is incapable of propelling the vehicle at a speed greater than 20 miles per hour on level ground.[104]
In general, electric bicycles are considered "bicycles", rather than motor vehicles, for purposes of the code. This implies that all bicycle regulations apply to electric bicycles including operation in bike lanes. Exceptions to this include a restriction of operation on sidewalks and that a license or permit is required if the rider is younger than 17 years of age(ORS 814.405 and 814.410).
I started riding mt bikes here in Oregon about 1987.
If you ride mt bike trails and even if it was 'legal' you will still catch hell from the un-motorized guys, they think you are cheating because you are not killing yourself pedaling. The trails are maintained by volunteer mt bike groups.
If you got involved with a local group and could sway the mindset of the collective, I would think would be the best way to get the word out that ebikes don't rip up the trails like ICE dirt bikes.
/cheers
