I don't see blanket pardons at a federal level because most federal convictions are for possession of mass amounts and/or for dealing, which is a whole different ball of wax. Nor are they usually limited to marijuana, unless it's something like charges against a "mule" who got caught. The usual federal drug sting nets the big guys, who have cocaine and heroin and meth, with the pot just sort of as an afterthought.

People who get caught with reasonable amounts of pot on federal land have usually gotten turned over to state authorities.