concurring in the judgment.
I cannot agree with the Court that the mineral reservations agreed to by the United States and the respondents in 1937 and 1939 are governed by some brooding omnipresence labeled federal common law. It seems clear to me, as a matter of law, not a matter of “choice” or “borrowing,” that when anyone, including the Federal Government, goes into a State and acquires real property, the nature and extent of the rights created are to be determined, in the absence of a specifically applicable federal statute, by the law of the State.
That was the very premise of the decision in Leiter Minerals, Inc. v. United States, 352 U. S. 220, 228-230 (1957), which remanded the case to the Court of Appeals with instructions to secure an authoritative construction of the state statute by the state courts, in order possibly to avoid deciding the federal constitutional issues. Other decisions of this Court lead to the same conclusion. United States v. Yazell, 382 U. S. 341, 352-358 (1966); United States v. Burnison, 339 U. S. 87, 89 (1950); Davies Warehouse Co. v. Bowles, 321 U. S. 144, 155 (1944); Sunderland v. United States, 266 U. S. 226, 232-233 (1924); Mason v. United States, 260 U. S. 545, 557-558 (1923); United States v. Fox, 94 U. S. 315, 320 (1877). Cf. Wallis v. Pan American Petroleum Corp., 384 U. S. 63 (1966).
Since I think the Government’s property acquisitions here are controlled by state law, the decisive question for me is whether the retroactive application of Louisiana Act 315 of 1940 to those acquisitions is constitutional.1 The 1937 deed of purchase and the 1939 condemnation judg*606ment were unequivocal: the mineral rights were reserved to the former owners of the land for a 10-year period, after which time — if certain conditions regarding exploration and production were not met — the reserved rights were to terminate, and complete fee title to the land, including the mineral rights, was to become vested in the United States. The Federal Government bargained for this contingent future interest in the minerals; it was clearly agreed to in the conveyances, and was thus reflected in the consideration paid by the Government to the former owners.
Yet the Court of Appeals held that Louisiana Act 315, which was enacted subsequent to those conveyances, operated to abrogate the agreed-upon terms of the mineral reservations by eliminating the Government’s future interest. This retroactive application of Act 315,1 believe, is a textbook example of a violation of Art. I, § 10, cl. 1, of the Constitution, which provides that no State shall pass any law “impairing the Obligation of Contracts.” 2
Accordingly, I concur in the judgment of the Court.
This case is a far cry from Home Building & Loan Assn. v. Blaisdell, 290 U. S. 398 (1934), which upheld, in the face of a challenge based on the Contract Clause, emergency state legislation enacted to cope with the extraordinary economic depression existing in 1934. The retroactive application of Louisiana Act 315 serves no such paramount state interest. Cf. City of El Paso v. Simmons, 379 U. S. 497 (1965).