Another source is to go to your friendly BLM office and purchase their maps for individual districts that cover areas you wish to explore. They plainly show the boundaries for private and public lands. The same goes for any areas you wish to explore within Humboldt-Toiyabe National Forest; requires a stop in at any ranger station, which are generally in a nearby town or city.
In most cases, if an established route goes across private land (not the land owner's driveway, but a route shown on a map), it is to be left accessible to those wishing to cross the land. Sometimes a bypass might be blazed by the land owner; often it simply continues through the fenced portion of his land. It will generally have a set of gates. Sometimes there is signage, such as the right to cross may be revoked at any time (generally applied and enforced it you piss off the land owner if you do something stupid - hey, we don't do that, right?
). As stated, leave gates as you found them.