36 C.F.R. § 4.2 : Parks, Forests, and Public Property — NATIONAL PARK SERVICE, DEPARTMENT OF THE INTERIOR — VEHICLES AND TRAFFIC SAFETY — State law applicable

(a) Unless specifically addressed by regulations in this chapter, traffic and the use of vehicles within a park area are governed by State law. State law that is now or may later be in effect is adopted and made a part of the regulations in this part.
(b) Violating a provision of State law is prohibited.

36 C.F.R. §4.2