I'm no expert on this, but see the link I posted above Wizard. Sometimes bureaucrats do not know that nudity is not illegal, as was the case with the apology from the Sheriff that Allen Bayliss obtained in the Angeles forest case in 2006. I found this older discussion on this board now almost 10 years old:
http://deepcreekhotsprings.net/dchs/forum/read.php?1,3277,3277#msg-3277
But other sources on line say that BLM land is federal land, and thus nudity is not illegal.
http://www.soakersforum.com/3/viewtopic.php?f=5&t=1980
http://www.blm.gov/ca/st/en/fo/cdd/cdd_supplementary.html
http://www.nytimes.com/gwire/2011/06/10/10greenwire-no-clothes-no-problem-on-some-blm-tracts-1630.html
Anyway, what part of the trail exactly crosses BLM land? is there a map to be seen?