The faces of Presidents George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln are carved on the mountain in the Black Hills region.
Statues of Father Junipero Serra have been repeatedly targeted since he was made a saint by Pope Francis in 2015.
Schlapp told his Twitter followers to "Pray for the USA."
The statue was spray-painted with the words "genocidal colonist," according to images shared on social media.
The debate over statue removal has re-emerged in Europe, largely motivated by the George Floyd protests in the U.S. but drawing on historic racism and existing racial inequalities in European nations.
Activists have been working to remove symbols of the Confederacy for years, but some states, such as Alabama, have enacted laws that make the process difficult.
The grave of James Stephen, who played a leading role in the abolition of slavery act, was covered in moss and the inscription was obscured.
"Monuments to men who advocated cruelty and barbarism to achieve such a plainly racist end are a grotesque affront to those ideals," House Speaker Nancy Pelosi wrote Wednesday.
The monument was erected as a symbol of gratitude for a loan from the Russian-Kyrgyz Development Fund.
A joint German/Egyptian excavation team has recovered relics and the remnants of a temple in Cairo.
Florida State Representative Mike Hill's bill would make it illegal to remove Confederate memorials, flags and other symbols, as well as the names of streets and schools honoring Confederate soldiers.
Some commentators argue that Britain should have chosen to honor a more radical feminist.
Experts believe that the statue was stolen before it was buried.
The team of experts said they found signs of a temple structure as well as other ancient objects
The next campaigns will be waged against the heroes of the revolutionary struggle.
"Confederate monuments have become symbols of modern white supremacy and neo-Nazism," the college's president said.
President Donald Trump has again criticized the removal of Confederate monuments across the country.
Monuments came down in Baltimore on Wednesday and Durham, North Carolina, on Monday.
The pieces were obtained by King Louis IX after the sacking of Constantinople.
Two amateur divers found 1,600-year-old Roman treasure off Israel's coast.
The Buddhas of Bamiyan have been resurrected, thanks to light projection technology and a generous couple.