QUICK FACTS
Where is it? Taklamakan Desert, China [38.459991514, 80.87050739]
What’s in the photo? A river and a mountain range forming a giant Y shape
Which satellite took the photo? Landsat 9
When was it taken? Sept. 11, 2025
This striking satellite snap shows a massive letter Y lurking in the heart of a recently transformed Chinese desert. The unusual shape is made up of a rocky ridge and a winding, gemstone-filled river and is also home to an important eighth-century fort.
The desert was previously considered a “biological void” — meaning it was almost completely devoid of life — due to its high temperatures and aridity. However, an ecological engineering project known as the Great Green Wall has planted more than 66 billion trees along the desert’s northern edge since 1974, which has transformed it into a carbon sink that soaks up large amounts of carbon dioxide, recent research revealed.
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The Y shape comprises two parts: the Hotan River, which stretches about 180 miles (290 kilometers) across the desert from south to north; and Marzatagh, a “wall-like” mountain ridge that stands around 600 feet (180 meters) above the surrounding sands and extends up to 90 miles (145 km) to the northwest, according to NASA’s Earth Observatory.
The Hotan River (sometimes called the Khotan River) is fed by glacial meltwater from the Kunlun Mountains south of Taklamakan and appears green due to vegetation that grows between its braided streams. Its waters are rich in both white and green nephrite, which are prized types of jade.
Marztagh is split into seams of reddish iron-rich rocks and paler sandstone, earning it the name Hongbaishan, meaning “red-white mountain” in Chinese. It also acts as a natural barrier for sand that gets blown against the rocky wall, creating a sea of rippling, crescent-shaped “barchan” dunes along its northern edge.
The confluence of drinking water, valuable gemstones and shelter from the elements made this location an important stop on the Silk Road — a massive network of trade routes running from east to west across Asia from the second century to the fifteenth century.
The point where the two features meet is home to the crumbled remains of a military fort, which likely dates to the eighth century.
Crumbling fort
The fortification, dubbed Mazar Tagh, was built on a hill at the intersection of the Y shape by the Tibetan Empire, which existed between A.D. 618 and 842 and covered most of the Tibetan Plateau, including parts of modern-day China, India and Afghanistan.
The site was first excavated in 1907 by Hungarian-British archaeologist Aurel Stein, who uncovered more than 1,500 document fragments, transcribed on both wood and paper, according to the The International Dunhuang Programme. These texts were written in multiple languages — including Khotanese, Uyghur and Sogdian — and document the soldiers’ experiences.
Other artifacts — including arrows, sheathes, shoes, dice, a comb and a pen — were also found at the site and are currently stored at the British Museum. However, the most impressive find was arguably a portrait of a “begging monk” painted on a wooden board, likely by a soldier. The monk was probably on a pilgrimage to an ancient Buddhist shrine that was built on the same hill.
Today, the hill is also home to an Islamic shrine.
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