The lunar souvenir was given to former Governor John Vanderhoof by the Nixon administration, which awarded bits of moon rubble to all 50 states and more than 130 foreign countries.
Vanderhoof is now 88 and living in Colorado. He has kept the rock on a plaque in his house and didn't think much of it until college students started looking for the moon rocks.
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But on Tuesday a Denver television station called to ask if he had Colorado's.
Vanderhoof joked that he had offered the rock to museums but no one was interested.
Its estimated value is $US5 million ($A5.91 million).
Another set of moon rocks collected in 1969 and awarded to Colorado was found in storage at the state history museum about a decade ago.
