Photo shows a rainbow arching across the Alien Valley Star Geological Park in Zhangye, Northwest China's Gansu Province. A geological known as "Alien Valley" in Zhangye, Northwest China's Gansu Province, is gaining popularity for its spectacular landforms. (Photo/China News Service)

Photo shows a rainbow arching across the Alien Valley Star Geological Park in Zhangye, Northwest China's Gansu Province. A geological known as "Alien Valley" in Zhangye, Northwest China's Gansu Province, is gaining popularity for its spectacular landforms. (Photo/China News Service)

Photo shows a rainbow arching across the Alien Valley Star Geological Park in Zhangye, Northwest China's Gansu Province. A geological known as "Alien Valley" in Zhangye, Northwest China's Gansu Province, is gaining popularity for its spectacular landforms. (Photo/China News Service)

Photo shows a rainbow arching across the Alien Valley Star Geological Park in Zhangye, Northwest China's Gansu Province. A geological known as "Alien Valley" in Zhangye, Northwest China's Gansu Province, is gaining popularity for its spectacular landforms. (Photo/China News Service)