I always thought of a national monument as one of these:
However, on the day after Christmas, we went to Muir Woods National Monument north of San Francisco. We figured there was a monument (i.e. statue or something similar) in the middle of the woods - however, the whole woods is called a “national monument”. I thought it weird but didn’t pursue it any further. However, I learned today that, on January 11, 1906, President Theodore Roosevelt declared the Grand Canyon a national MONUMENT. Weird.
But this is why .. “Though a region could be given national park status--indicating that all private development on that land was illegal--only by an act of Congress, Roosevelt cut down on red tape by beginning a new presidential practice of granting a similar "national monument" designation to some of the West's greatest treasures.” ... from here.
This is why I get these e-mails every morning from History.com (so I can learn something).