Unfortunately there are very few gravel roads in Sauk County... But I notice you enjoy Mountain Biking - The Wildside guys put a LOT of effort into Devil's Head mountain bike trails, little more on the enduro/all mountain style of riding, check those out this summer. Devil's Head (<10miles southeast of Baraboo) is a ski resort, so bike up or take the chair lift, your call! Also, Mirror Lake State Park (about 15miles northwest of Baraboo) has some amazing XC/single track if that's more your style. I would say you could even ride a gravel bike on some of the trails, just watch out for the occasional sand pit.
The Wildside associates and Sauk area people are working on the SPRA efforts with CORP IMBA chapter.
Devil’s head has always been up and down as far as support for the trails and it doesn’t look like anyone’s got a passion for it these days. The only ski place where the trails have been sustainable is Blackhawk Ski Club where memberships start at $25. Some cross and gravel riders do that and Pleasant View on drop bar bikes. I’ve done it but it’s SO much better on a MTB if you know how to fly.
On the whole, population, dairy industry and tourism mean a lot of paved roads so checking in with Wildside would be my suggestion. They’re great people.