Videos and images showed bright red spray painting on the column located in the Lone Fir Cemetery of the words: 'F**k USA.'
A statue that was mounted on top of the structure was also toppled and seen on the ground covered in red paint.
The memorial, which was erected in 1903, honors soldiers of the Civil, Spanish-American, Mexican, and Indian wars, according to the cemetery's website.
In addition to the vandalized memorial, at least 10 businesses in Portland were damaged overnight.
Portland police claim they responded to reports of a group of people smashing windows and spray-painting graffiti on buildings.
They said that multiple callers reported seeing a group of people dressed in black and moving west along Hawthorne, breaking out windows as they went.
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Businesses sustaining damage include banks, an auto service center, a shipping store and other storefronts, police added.
Officers said they found damage to at least 10 businesses on Hawthorne between Southeast 33rd and Southeast 41st Avenue. They estimated several thousand dollars’ worth of damage.
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There were also reports of statues being toppled and graffiti sprayed, in two different parks around the city. Police did not immediately confirm those reports.
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Authorities said they arrested 24-year-old Chester Hester, 38-year-old Nicole Noriega and 23-year-old Bailey Willack. One of the group members was carrying a semi-automatic pistol and could face weapons charges.
They were booked into the Multnomah County Jail, and each face 10 counts of first-degree criminal mischief. It’s not clear if they have attorneys.
Authorities didn’t provide a cost estimate of the damage.
Police say that, based on statements from witnesses, more people were likely involved, and they plan to continue investigating.
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The protest took place after a call to action on Wednesday urged indigenous protesters to attack symbols of colonialism, capitalism, and gentrification ahead of Thanksgiving.
Members of Antifa said in a Facebook post that they're 'tired of seeing white people celebrate the genocide of our ancestors'.
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'F**k thanksgiving,' the post reads. 'Organize your own direct action.'
It's unclear whether the three individuals arrested identify as members of the anti-fascist protest movement.
Protesters have stated their plans to continue the protest of colonization, capitalism and gentrification they said Thanksgiving represents.
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Portland has been the site of more than 100 nights of protests - many turning violent - following the killing of George Floyd by Minneapolis police in May.
The city was the scene of almost nightly clashes between Black Lives Matter protesters and local and federal law enforcement over the summer.
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