The singletrack trails in the Molalla Recreation Corridor are closed to bikes and horses when the trails are wet, and also between October 15 and April 15 every year. The doubletrack is open year-round. Singletrack trails are marked as "Seasonal" on signs.
The Huckleberry Trail is gravel doubletrack that forms a sort of backbone for the trail system. It will likely be either at the beginning or end of your ride. Some parts are mostly flat, while other parts are inclined. Because it is an old logging roadbed, the grade is never extremely steep. It shares a lot of the same vibes as the Leif Erikson Drive in Portland's Forest Park.
Along the trail is Annie's Cabin, a public hiking shelter that can be used by anyone. Not much is furnished inside, but a fire ring and picnic table are present. Be careful with that outside locking door though... kinda eerie.
Huckleberry Trail extends further south for a short distance but there is no more singletrack down that way so you likely won't be compelled to head down there.