CA Civ Proc Code Section 1240.150

Whenever a part of a larger parcel of property is to be acquired by a public entity for public use and the remainder, or a portion of the remainder, will be left in such size, shape, or condition as to be of little value to its owner or to give rise to a claim for severance or other damages, the public entity may acquire the remainder, or portion of the remainder, by any means (including eminent domain) expressly consented to by the owner.