Nancy -
There a state-scaled public lands maps, but they generally do not allow a person to determine specific sections. The best sources are maps of national forests which identify adjacent BLM and other public lands. Since the national forest lands are more appealing for cycling, most of us tend to be in areas covered by these maps. If not - such as in west-central Nevada or south-central Wyoming, then there are BLM maps which show public lands.
It would be nice if all of these maps were available online, but they are not yet. You have to buy them. Most national forest maps are now plastic - which is great for cyclists. BLM maps aren't. The national forests in California have put all of their maps online.
http://www.fs.fed.us/r5/forestvisitormaps/
Happy Trails - - - J