It was commemorating
"the birthplace of the American Armored Forces". Fifty pounds of
earth taken from the 48 states, Hawaii and Alaska will be scattered around the roots of the tankers "Memorial Pine Tree", earth steeped in the blood of American soldiers from the Revolution through the great wars of our republic. From South Carolina comes soil from the Kings Mountain Battlefield, where the British were defeated by American troops on Oct. 7, 1780.
Texas sends soil from the Alamo, where Davy Crockett, Col. James Bowie, and a handful of Americans were slaughtered by Santa Anna in 1835, and from San Jacinto where on April 21, 1836. the Texans won their independence from Mexico. Louisiana -soil was dug from Chalmette Battlefield where Andrew Jackson won the Battle of New Orleans by whipping the British forces, January 8, 1815, after the treaty at Ghent had already been signed. The North Dakota earth is that trod by General George A. Custer at Fort Lincoln as he set out with his 7th cavalry in 1876 to face massacre at the hands of Sitting Bull. From Patton's Home From Massachusetts has come earth from the home of General George S. Patton, one of the world's great tank commanders; from Vermont, ground from Calvin Coolidge's homestead. Colorado is represented by "land from the home of Mrs. John S. Doud, mother of Mrs. D. D. Eisenhower. Nome's Golden Beach, black and ruby sand flecked with gold, Ft. Knox, Ky., with earth scopped up in a mint julep cup. Florida, with soil from a historic cannon outside the Jacksonville city hall, are other sites whose earth will form a portion of the new memorial.
source-
https://www.newspapers.com/newspage/45978809/
Edit - Your source supports your answer that the marker commemorates the birthplace of the American Armored Forces, so this is a correct answer.
Hoosier