TheCalifornia Department of Motor Vehicles, Vehicle Code, Division 12, Chapter 4Section 26700 it states.

"26700.(a) Except as provided in subdivision (b), a passenger vehicle, other than a motorcycle, and every bus, motortruck or truck tractor, and every firetruck, fire engine or other fire apparatus, whether publicly or privately owned, shall be equipped with an adequate windshield.

(b) Subdivision (a) does not apply to any vehicle issued identification plates pursuant to Section 5004 which was not required to be equipped with a windshield at the time it was first sold or registered under the laws of this state, another state, or foreign jurisdiction.

Amended Ch. 222, Stats. 1983. Effective January 1, 1984. "

Based on this information, a windshield is required by California to legally operate a car. The windshield is an important safety component for your vehicle and most states require a windshield and working windshield wipers. California requires both of these items.