California Code, Code of Civil Procedure - CCP § 1263.205

(a) As used in this article, “improvements pertaining to the realty” include any machinery or equipment installed for use on property taken by eminent domain, or on the remainder if such property is part of a larger parcel, that cannot be removed without a substantial economic loss or without substantial damage to the property on which it is installed, regardless of the method of installation.

(b) In determining whether particular property can be removed “without a substantial economic loss” within the meaning of this section, the value of the property in place considered as a part of the realty should be compared with its value if it were removed and sold.