There are plenty of public lands on which to explore and there are also private claims which should be respected. It is not necessarily an easy dig but in my two times visiting the most disturbing part is the total lack of assistance by the USFS. Both in Missoula and Lolo Pass all parties were less than helpful and in fact I wouldnt even mention that you are looking for crystals. Just buy the map for the general area which has some of the forest service roads - atleast the ones you will need. The best approach is from the Idaho side down to Granite Creek. You might also try the road down Crooked Creek in Idaho. I found some small white phantom quartz in some of the diggings there.
Remember if you dig a hole fill it back in again. You will understand if you make it to the main collecting area along Granite Ridge. All of the popular rockhound collecting books also have much to be desired since none of them even show you how to get to any of the classic local collecting areas.
Directions: As a service to fellow collectors I have created a detailed downloadable map in PDF format. To get a detailed map of the collecting area click here.