In Iowa a Class B road is an earthen road. According to a friend of mine from Iowa it started with the Mn. vs. Iowa football game down there 100 years ago. I just looked it up and he is right 1922 and Mn. lost. The roads at the time were all earthen (not graveled) and it rained during the game soaking the roads making them impassable. Thousands of people were stuck in the roads on the way home in freezing temps and they decided it was time to start work on their road system. They still have a lot of gravel roads but a few earthen as well. So does Mn. and many other States but Iowa is unique in their classification. Then again there is Wi. where County roads have letters instead of numbers so who am I to judge.
Hiluxforever likely knows this but you can pull up and download Iowa County road maps like most States on line.
Iowa County Roads Index The Class B roads are in green and earthen roads. If you look at the color pdf option. You also have the option of AutoCAD (DWG) files and MicroStation Design.
That is because Avenza Maps has become the defacto standard for government agencies from Federal to State including Counties as of late. The app only runs on mobile devices but of course if you have the native app for the file you can also read it, georeferenced PDF files are the most common on websites. You don't need cell phone reception to utilize the GPS functionality of your phone with them which is good as most places I go have no cell phone reception.
The complete National Forest System is regulated for Motor Vehicle Use and you can download
Motor Vehicle Use Maps (MVUM) for the entire Country on National Forest Lands.
There is 6 million square miles in Superior National Forest alone, with the State and County public land you are looking at more than 10 million square million miles in the Mn. Arrowhead. The NF roads are regulated and with today being May 1 many of them open today for the first time since last year. Doesn't mean you will be able to drive down them many you can not. Washouts, beaver dams causing road flooding, stream changes over the winter, and downed trees. And some have been overgrown for years and will continue to be until they log a section of land off a spur road. But it is just a Forest Road they said LOL. I carry a chain saw during hunting season not to clear a road, I'm not there to play Paul Bunyan. But in case of blowdowns and have to cut my way back out.