According to Bloomberg https://about.bgov.com/news/old-capitol-stones-to-be-stored-away-after-decades-piled-in-park/ "Old Capitol Stones to Be Stored Away After Decades in Park" the stones removed from the US Capitol for the 1950s East Front renovation are to be moved and stored at Fort Meade.
The move will mark the end of an unofficial history exhibit, touted as a hidden treasure in Rock Creek Park by publications including Washingtonian and Atlas Obscura. The stones were removed during Capitol renovations from 1958-62 and kept at the nearby Capitol Power Plant until officials dumped them in the park nearly a half-century ago.
“The stones are being moved at the request of the National Park Service for safety, realignment and preservation purposes,” Kiren Marshall, senior communications specialist for the Architect of the Capitol, said in an email. “They are being moved to the AOC’s area at Ft. Meade. The public will not have access to the stones there.”
The National Park Service issued a permit to the Architect of the Capitol, which owns the stones, to remove them, Brian Joyner, deputy superintendent of Rock Creek Park, said in an email. The park is managed by the National Park Service.