A general shooting ban on federal lands is currently interpreted as a trigger for PC 12031, so LOC would probably not be legal in those areas. An exception to this would be if one possessed a valid hunting permit while in lawful pursuit of in-season game, such as coyote. Even when there is a general shooting ban, hunting tends to remain legal, though that may not always be the case. UOC would always be legal.
The other school of thought on the matter is that the only shooting bans which may trigger 12031 are county-issued bans, and that state and federal bans do not apply. This is supported by the Attorney General's 1968 memo, as well as the decisions of People v. Knight, People v. Young and People v. Segura. If that were the case, then it would mean that absent any county-issued bans, it would be legal to open carry loaded in Yosemite, even though federal law bans shooting in that park. This is not well established by case law, and it is not recommend that one do this at this time, unless one is prepared to fight a criminal case at their own expense.
If in doubt, carry unloaded.