I bet someone at Skamania Lodge could tell you by phone, like either the concierge or the person in the US Forest Service information shop at the lodge.
High-tension power lines run east-west for many miles through the gorge with rough, double-track dirt and side trails under them, and pass by the lodge just uphill from the golf course. I strongly suspect you can access them without even a car ride; I know you can with a drive up Skaar Road above Stevenson.
Wind River Road up through Carson has many possibilities. Check it out on Google Maps. If you go left at Stabler and then right at the Hemlock Ranger Station you'll be in an area with experimental forests, old growth, and plenty of gated spur roads, and the Crest Trail crosses through there. Should be some single track but I don't know for sure what's available. Wind River Road continues up into NFR 30 with several other side roads, but I would expect snow on spurs and trails even below Old Man Pass.
Camas Bike & Sport
has rentals; good shop, good folks. Hood River probably has something, too. I don't think there's a bike shop in Stevenson.
I'm guessing that many of the trails in these two guides will still be snowed under in March:
Best for last?? Check out NWTA's nicely done wiki and map: