A U.S. Park Police officer is stationed inside the chamber of the memorial, which is open 24 hours a day. Cleanup is expected to continue Monday.
The National Park Service is confident the memorial can be restored to the condition it was in before the vandalism.
Jamie McDaniel, of Stafford, Va., tells NBC 4 she and a friend discovered the vandalism and brought it to the attention of Park Police.
"I looked, and was like, 'That's green paint.' It was splattered everywhere," McDaniel says.
McDaniel looked around, and saw two Mountain Dew soda bottles that had been filled with paint - one with green, one with white.
She found a Park Police officer.
"I went up to him and told him, 'You've got to come in here. You're never going to believe this. Someone has done something to the memorial'," McDaniel recalls.
She was outraged.
"It was almost like someone burned the flag. Immediately we were both angry, and like, 'Who would be so stupid?'" she says.
Park Police are reviewing surveillance video. They have not released it to the public, or identified any possible suspects.
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