Neil Armstrong and Buzz Aldrin plant the US flag on the surface of the moon
California has named a new site a state historical resource - despite the fact that it is not on Earth, never mind in the US state.
The site where Apollo 11 landed on the Moon in 1969, the first US landing, is now included on the state's register.
The unusual move by the California State Historical Resources Commission aims to protect more than 100 items left by US astronauts on the Moon.
They include tools, a flag, footprints, food bags and bags of human waste.
The commission said California firms had worked on the Apollo project and their efforts had a historical value to the state.
"It has a significance that goes way further than whether it came from a quarter million miles away or not," state historic preservation officer Milford Wayne Donaldson was quoted as saying by the New York Times newspaper.
"They are all parts of the event," he said.
The designation applies to everything left on the Moon by astronauts Neil Armstrong - the first man to walk on the Moon - and Buzz Aldrin, with a total weight of 5,000 lbs (2,270 kg).
A number of items were jettisoned by the mission in order to make their module lighter for the take-off which began their journey back to Earth.
However, the moon's surface is not included in the designation, because under international law no country or state can make a claim to it.
The move aims to protect the site in the face of possible lunar missions in the future by other nations.
Several other US states which were involved in the Apollo project are also reportedly seeking to protect the landing site.