California Code, Government Code - GOV § 50558

If the improvement is useful and necessary for the rendition of a service to the local agency, the legislative body shall provide that the sale is conditional upon the purchaser maintaining and operating the improvement for the purpose of providing such service. The contract of sale shall prescribe the period of time during which such condition shall be operative and may prescribe circumstances under which it may be terminated by the parties prior to the expiration of such time.