California Code, Government Code - GOV § 51051

(a) “Grant of an open-space easement” means a grant by an instrument whereby the owner relinquishes to the public, either in perpetuity or for a term of years, the right to construct improvements upon the land except as may be expressly reserved in the instrument and which contains a covenant with the city or county, running with the land, either in perpetuity or for a term of years, not to construct or permit the construction of any improvements, except as that right is expressly reserved in the instrument and except for public service facilities installed for the benefit of the land subject to any covenant or public service facilities installed pursuant to an authorization by the governing body of the city or county or the Public Utilities Commission.

Any such reservation shall be consistent with the purposes of this chapter or with the findings of the county or city pursuant to Section 51056 and shall not permit any action that will materially impair the open-space character of the land.

(b) “Owner” means any lessee or trustee, if the expiration of the lease or trust occurs at a time later than the expiration of the easement or any extension thereof.