Congressional approval is only necessary for "Wilderness" areas. There are millions of acres in Colorado on USFS and BLM lands that are closed to over the snow travel. These are enforcable, you could get a ticket for travelling in designated non-motorized areas. They are lightly enforced however. Problem is they are often heavily used areas with lots of ski bastards around who are quick to call the ranger.
Read the maps, then at least you know where you are supposed to be. Let you conscience be your guide. I'm not going to preach to anybody about staying out of any parcel of public land. I agree, it is public, intended for public use and the closed areas represent discrimination of a select user group regardless of how the forest managers justify it. Funny how this is the only remaining segregation allowed in our country. Doesn't fly anywhere but on "public" lands, figure that one out.
Bottom line, then can and do close areas. The can enforce the closures, they rarely do. My advice, join the Colorado Snowmobile Association. We have 20,000 registered sleds in the state and 2000 members. The forest manangers are starting to hear us, but we need everybody's help.
Enjoy your ride!