Don't know about unpaved roads but the one from the coal plant (Big Hanaford Rd) thru Tono to Bucoda is a fun little paved road. Watch out for dips and repairs
. I rode some of those last summer from Alpha to Bucoda bring along a GPS because some of them dead end way off the beaten path without warning.
Some day we need to explore all the dirt roads in/around Mt. St. Helens between Nf-25 and I-5 been wanting to do that for awhile.