Rarely mentioned National Parks and Monuments.

eubank wrote:
It may be worth noting that not all national monuments are part of the National Park Service (and, therefore, not listed on their website). Rio Grande del Norte is one such.

Lynn

Quite right that's why I mentioned the list on Wiki. They also have lists of parks, memorials and historic sites. They have a complete list of lands under the NPS system. There are 418 units. That list includes discontinued parks and monuments which disproves the claim that 'once in the system, never out'.