"natural monuments" is a perfectly correct and usable phrase in written English.
You can use it to refer to any naturally occurring structure that has some important historical or cultural significance, such as a mountain, a desert canyon, or a cave. For example: "The Grand Canyon is one of the United States' most impressive natural monuments."
Protected areas network in Kosovo consist of: one national park, 11 nature reserves, two protected landscapes and 82 natural monuments with different natural characteristics: botanical, geographical, geomorphologic, hydrological etc.
In Slovenia, the marine and coastal protected nature areas are the Sečovlje Salina Landscape Park, Strunjan Landscape Park, Škocjan Inlet Nature Reserve, and the Debeli Rtič, Cape Madona and Lakes in Fiesa natural monuments.
Their austere elegance is in keeping with the views of man-made and natural monuments she has shot in Asia and Africa.
The austere elegance of these photographs is in keeping with the manmade and natural monuments she has shot in Asia and Africa, but the icebergs are more mysteriously elemental (Glueck).
Residents say more than 100,000 people arrive by car, motorcycle and recreational vehicle in the summer, drawn by natural monuments like the vast Salmon Glacier, about 18 miles from town and over the Canadian border.
But now Lebanon's cedar trees (Cedrus libani), described in the Scriptures as "the glory of Lebanon" and by the 19th-century French Romantic poet, Alphonse de Lamartine, as "the most famous natural monuments in the world", face a new threat in the form of climate change.
The karstic Bicaz Gorges are a natural monument.
In 1931 the Japanese government designated the breed as a "natural monument".
Lake Roşu, another natural monument, contains a forest that was inundated during a landslide in 1938.
A protected natural monument, chock-full of rare plant, bird and reptile species.
Once severely threatened because of overhunting and habitat loss, it was designated as a "special natural monument" in 1955.
