The rhino, named Angalifu, died at the age of 44, with the cause of the death said to have been old age.
“Angalifu’s death is a tremendous loss to all of us,” said safari park curator Randy Rieches in a statement.
Northern white rhinos are near extinction due to poaching. Their horns are valued as dagger handles and seen as an aphrodisiac.
San Diego Zoo Safari Park had unsuccessfully attempted to mate Angalifu with Zola, the other female northern white rhino at the zoo.
Barbara Durrant, from the San Diego Zoo Institute of Conservation Research, said in a statement: "More than two decades ago, we started working with species here at the Safari Park.
“Unfortunately, we only had three rhinos here at the park and they were all of an advanced age. We were not able to get them to breed and we have been sadly watching their species being exterminated in the wild.”
Last week, conservationists at the Old Pejeta animal sanctuary in Kenya also found that their northern white rhinos will be unable to reproduce naturally.
An experiment, involving in vitro fertilisation with a southern white rhino surrogate mother, will now take place in an attempt to keep the species alive.
By Ruchi Singh
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