It should be, but to tell you the truth...no one can give you a clear answer.  Here's why.  The Federal Government passed a law saying that the National Park System can't outlaw open carry of firearms if they are possessed in compliance with state law (see below).  That was all well and good until Jerry Brown helped pass a stupid law last year banning open carry in california (read about that here: http://www.huffingtonpost.com/2011/10/10/california-open-carry-law_n_1003843.html).So, since Brown made open carry illegal in CA, even though the legislative intent of the federal law was to ease regulations--it appears that to legally carry in a national park, you have to be in compliance with the regulations of the state in which that park lies, so open carry in a national park within the state of Calfiornia would be illegal by extension--unless you are law enforcement or have a CCW Permit.  Additionally, open carry in most CA state parks and some BLM parks is illegal.  This is all totally rediculous, especially when one considers the heritage of California. I would recommend contacting the park ranger station of the park that you are looking to visit and asking them if in their opinion open carry is legal within their park.  I would also leave the firearm in you car, go into the ranger station when you arrive and clear it with the rangers on staff to make sure everybody's on the same page.Text of Federal Law:(3) Section 27.42 of title 50, Code of Federal Regulations, provides that, except in special circumstances, citizens of the United States may not ``possess, use, or transport firearms on national wildlife refuges'' of the United States Fish and Wildlife Service. (4) The regulations described in paragraphs (2) and (3) prevent individuals complying with Federal and State laws from exercising the second amendment rights of the individuals while at units of-- (A) the National Park System; and (B) the National Wildlife Refuge System. (5) The existence of different laws relating to the transportation and possession of firearms at different units of the National Park System and the National Wildlife Refuge System entrapped law-abiding gun owners while at units of the National Park System and the National Wildlife Refuge System. (6) Although the Bush administration issued new regulations relating to the Second Amendment rights of law-abiding citizens in units of the National Park System and National Wildlife Refuge System that went into effect on January 9, 2009-- (A) on March 19, 2009, the United States District Court for the District of Columbia granted a preliminary injunction with respect to the implementation and enforcement of the new regulations; and (B) the new regulations-- (i) are under review by the administration; and (ii) may be altered. (7) Congress needs to weigh in on the new regulations to ensure that unelected bureaucrats and judges cannot again override the Second Amendment rights of law-abiding citizens on 83,600,000 acres of National Park System land and 90,790,000 acres of land under the jurisdiction of the United States Fish and Wildlife Service. (8) The Federal laws should make it clear that the second amendment rights of an individual at a unit of the National Park System or the National Wildlife Refuge System should not be infringed. (b) Protecting the Right of Individuals To Bear arms in Units of the National Park System and the National Wildlife Refuge System.--The Secretary of the Interior shall not promulgate or enforce any regulation that prohibits an individual from possessing a firearm including an assembled or functional firearm in any unit of the National Park System or the National Wildlife Refuge System if-- (1) the individual is not otherwise prohibited by law from possessing the firearm; and (2) the possession of the firearm is in compliance with the law of the State in which the unit of the National Park System or the National Wildlife Refuge System is located.