PLEASE NOTE: 8-18-12 Big bike bypass revised. Track is in post #17.
Upon review and a re-ride, I've come to the conclusion that calling this "big-bike friendly" may lead some into peril. Accordingly, I am working to identify a specific big-bike bypass around the "worst" (may be best if you like sand) sections. MILITARY PASS ROAD IS NOT A VIABLE BYPASS AROUND THE SAND ON A FULLY LOADED BIG BIKE UNLESS YOU LIKE THE SAND!
Understand, I laid this route out on a KTM 990 Adventure and I've ridden every foot of it on that bike, but there are a couple of sections that were not very much fun.
Sequential tracks for a DS loop beginning and ending at the Lake Siskyou Campground near Mount Shasta City.
Conditions on these routes may change significantly with weather, use, and runoff. There are some sections with significant sand, some rocks and plenty of brush which may damage yourself, your equipment, or your attitude.
In other words, use at your own risk and don't whine to me.
That said, I laid the route out on a KTM 990 adventure and I have seriously short legs. I'd
call it big-bike mostly-friendly, but YMMV on that.
Total Distance is about 115 miles depending on whether you follow the paved return along the river or take the added-dirt return, and how much exploring you do along the way.
It's roughly 50/50 scenic pavement and dirt two-track. Dirt ranges from easy broken pavement to rocks and sand as noted above. Don't forget to look around, there is some serious scenery on this route.