If you aren't sure if you're on public land, you must have written permission from the private landowner. The Caribou Wilderness area is available for those who may wish for solitude but not high deer densities. Many other major roads, county, US Forest Service and others, provide basic access throughout the zone. The best maps of the area are the maps of the Lassen National Forest or USGS topographic maps. There are also maps of the specific wilderness areas if you wish to hunt there.
USGS maps are commonly available from stationary and engineering stores.
Remember, it's your responsibility to know what lands you are on. Trespass on private lands will be enforced. It is difficult to get around in some of this country in a vehicle, particularly in some of Tehama County and the High Lakes area of western Plumas County. Horses may be of use in some of the inaccessible areas but be aware that you must take in your own feed. The weather for the later seasons should be colder and storms should be expected, including the possibility of snow.