(Portland, OR) -- Portland Parks and Recreation says a new memorial bust at Mt. Tabor Park remains a mystery. Authorities say an unknown artist has placed a bust of York where the Harvey Scott statue was toppled last fall. York was William Clark's slave. He was a member of the Lewis and Clark expedition and is also known as the first African American to cross North America. Parks and Rec say they will keep the installment in place as long as it's secure.