The Flaming Mountains (Chinese: 火焰山; pinyin: huǒyànshān) or Gaochang Mountains are barren, eroded, red sandstone hills in Tian Shan Mountain range, Xinjiang, China. They lie near the northern rim of the Taklamakan Desert and east of the city of Turpan. Their striking gullies and trenches caused by erosion of the red sandstone bedrock give the mountains a flaming appearance at certain times of the day.
The mountains are approximately 100 kilometres (60 mi) long and 5–10 km (3–6 mi) wide, crossing the Turpan Depression from east to west. The average height of the Flaming Mountains is 500 m (1,600 ft), with some peaks reaching over 800 m (2,600 ft). The mountain climate is harsh, and the extremely high summer temperatures make this the hottest spot in China, frequently reaching 50 °C (122 °F) or higher. One of the largest thermometers in China—a popular tourist spot—is on display adjacent to the mountain, tracking the surrounding air temperature.
A number of important palaeontological remains have been found in the area. (See e.g. Lianmuqin Formation, Subashi Formation).