The group that does two centuries each summer here added a gravel ride two years ago. They did it halfhearted, no supported rest stops or sag support, and no route markings. They do provide a route you can download. The elevation gain in 100 miles of gravel is like 6,000 feet.
I haven’t tried it, I usually just ride their 65 mile road ride with well stocked rest stops and sag support and markings on the road to show the route.
I think they made it hard so nobody would sign up and they could drop the gravel ride because nobody signed up. Guess what? The gravel riders loved the ride and it had twice as many riders the second year.
They don’t provide anything but a route download for the gravel ride. I’m not paying $30 for that. I downloaded the route, I might try it on my own sometime.