No, didn't know about these.
Yes, have visited many National Monuments. Love 'em.
Yes, I will visit them if I'm ever nearby.
That is the trouble with National Monuments. Unlike National Parks, they're not usually a "destination spot." That may be the only trouble with them... and that there could be lots more listed. Apparently in WA there is only Mt. St. Helens. Been there several times, it is remarkable though I'm saddened at the inability of the government to maintain their buildings & staff. Lots of it is now run by volunteers. The privately-run visitor center just outside the area is better funded, I think, and definitely worth seeing.
Here's a List of Other National Monuments of the USA
Hmmm, I see that Devil's Tower is a National Monument. A friend visiting from Minnesota said he stopped there and it was spectacular. I asked if it was bigger than he expected (as the Grand Canyon is) and he laughed, "Yes, it is!" I want to see!
The UK (I noticed, while searching for that link) has national monuments. It would be interesting to find out if other countries had these and if they had similar goals and administration. One thing we don't seem to have in the USA is a National Trust.