Cal. Streets and Highways Code § 280

(a) There is created within the state scenic highway system a system of California Historic Parkways. (b) California Historic Parkways are freeways that meet all of the following criteria: (1) The original construction was completed prior to 1945. (2) The department or the Office of Historic Preservation in the Department of Parks and Recreation announces or recognizes features of historical significance, including notable landmarks, historical sites, or natural or human achievements that exist or that occurred during the original construction of the parkway or in the immediately adjacent land area through which the parkway currently passes. (3) Any portion of the highway or corridor is bounded on one or both sides by federal, state, or local parkland, Native American lands or monuments, or other open space, greenbelt areas, natural habitat or wildlife preserves, or similar acreage used for or dedicated to historical or recreational uses. (4) Any portion of the highway is traversed, at the time of designation and by the department’s best count or estimate using existing information, by not less than 40,000 vehicles per day on an annual daily average basis.