Utah Power and Light Co. v. United States 243 U.S. 389 (1917) UPLC built a power plant in a National Forest in Utah. They got permission from Utah, but never bothered to ask the Federal government. Once the Federal government realized what happened, they sued for an injunction. UPLC argued that they had gotten permission from the State, and that should be good enough. UPLC argued that Utah law should apply because there had been no cession of jurisdiction by the State under the Enclave Clause (Art. 1 §8, cl. 17). Therefore, the Federal government did not have the right to preempt State law. See Fort Leavenworth R. Co. v. Lowe (114 U.S. 525 (1885)) for more info on how the Enclave Clause is applied. The US Supreme Court found for the US and granted the injunction. The US Supreme Court found that that if State law on Federal property conflicts with Federal law, then the Property Clause (Article IV, §3, cl. 2), and the Supremacy Clause (Article IV, §2) trump State law. The Court didn't base their decision on the Enclave Clause at all. There aren't very many modern cases regarding the Enclave Clause. It is much more common for the Federal government invoke a combination of the Property Clause and the Supremacy Clause to keep the States from regulating Federal land. For example, see Kleppe v. New Mexico (426 U.S. 529 (1976)).