Wow, that seems totally inappropriate to me too! I've hiked part of the Rho Ridge trail, and part of it has the spur that goes up to the Hawk Mtn cabin-I love that place!. Great, now we will get OHVers trashing that place, too.......It apparently isn't the only trail in the Mt Hood Forest that OHVs are allowed (although it looks like the only one in the Clackamas district):
All
off-highway vehicles are prohibited from going off road and
are also prohibited from using all national forest system
trails including: the McCubbins Gulch Trail System (Trails
# 575, 576, 577), Rocky Butte Trail #476, and N. Section Line
Trail #451 located on Barlow Ranger District, and the Rhododendron
Ridge (Rho Ridge) Trail #564 located south of Estacada. These
trails will be re-opened later in the year when the fire danger
has subsided.