premise: The Washington Monument is 554.5 ft tall.
hypothesis: Washington Monument . Located almost due east of the Reflecting Pool and the Lincoln Memorial , the monument , made of marble , granite , and bluestone gneiss , is both the world 's tallest stone structure and the world 's tallest obelisk , standing 554 ft tall according to the National Geodetic Survey ( measured 2013 -- 14 ) or 555 ft tall according to the National Park Service ( measured 1884 ) .