When not less than one thousand two hundred acres of the non-Federal lands hereinafter described (together with improvements thereon) and known as the Pea Ridge Battlefield, near Bentonville, Arkansas, shall have been acquired and transferred free and clear of all encumbrances to the United States without expense to the Federal Government, such areas shall be, and are hereby, dedicated and set apart as a unit of the National Park System for the benefit and enjoyment of the people of the United States, under the name of the Pea Ridge National Military Park.