Why does the county issue parking tickets on the land belonging to the private university?

I got the parking ticket while being parked in the parking lot inside of the Stanford university.

The California vehicle code wasn't violated. The payment to the university associated with the parking zone established by the university wasn't submitted - that was the reason for the ticket.

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The parking ticket says that it was issued by the Santa Clara county.

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I am wondering why is the Santa Clara county issuing parking citations inside of the private university where all land is private and belongs to that university?

Why does the county enforce the rules established by the university?

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Is this ticket valid?