The Flaming Mountains (Gaochang Mountains) are barren, eroded, red sandstone hills in the Tian Shan Mountain range in the Xinjiang Autonomous Region, China. They lie near the northern rim of the Taklamakan Desert and east of the city of Turpan. Their striking gullies and trenches have been etched by years of volcanic activity that caused molten lava to course down the mountainsides, giving the mountains a flaming appearance at certain times of the day. The mountains are 98 kilometers (61 mi) long and 9 kilometers (5.6 mi) wide and cross the Tarim Basin from east to west. The average height of the Flaming Mountains is 500 meters (1640 ft). The mountain climate is harsh and the temperature is extremely hot in the summer, the hottest spot in China with frequent temperature reaching over 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.