The exterior boundaries of the Shasta National Forest in the State of California are hereby extended to include the lands described in the Act of March 19, 1948 (62 Stat. 83), and sections 22 and 27, township 35 north, range 1 west, Mount Diablo base and meridian. The exterior boundaries of the Trinity National Forest in the State of California are hereby extended to include all of sections 4, 5, and 8, the east half and the northwest quarter of section 6, the east half of section 7, the northwest quarter of section 17, and the northeast quarter of section 18, township 33 north, range 8 west, Mount Diablo base and meridian. Subject to any valid claim or entry now existing and hereafter legally maintained, all public lands of the United States and all lands of the United States heretofore or hereafter acquired or reserved for use in connection with the Shasta, Clair Engle, or Lewiston Reservoirs of the Central Valley project within the exterior boundaries of the Shasta and Trinity National Forests which have not heretofore been added to and made a part of such forests, and all lands of the United States acquired for the purposes of the recreation area in the Shasta or Clair Engle-Lewiston units are hereby added to and made a part of the respective national forests within which they are situated: Provided, That lands within the flow lines of any reservoir operated and maintained by the Department of the Interior or otherwise needed or used for the operation of the Central Valley project shall continue to be administered by the Secretary of the Interior to the extent he determines to be required for such operation.