Wikipedia about the Washington Monument:

"In the lower third, marble from Baltimore County, Maryland, followed by a narrow zone of marble from Sheffield, Massachusetts, and, in the upper part, the so-called Cockeysville Marble."

What it doesn't say is that the MD Grand Lodge of Freemason's HQ, established in 1787, is in Cockeysville. None of this is proof, but connections are interesting, and I'm having a hard time believing it's a conspiracy theory.