Landforms at Zhangye Danxia Landform Geological Park in Zhangye City, northwest China's Gansu Province, on July 7, 2014. Danxia, which means “rosy cloud,” is a special landform formed from reddish sandstone that has been eroded over time into a series of mountains surrounded by curvaceous cliffs and many unusual rock formations. #

The Maijishan Grottoes in the city of Tianshui, Gansu Province, on August 12, 2015. The Maijishan Grottoes are a series of 194 caves cut in the side of the hill of Majishan in Tianshui. This example of rock-cut architecture contains over 7,200 Buddhist sculptures and over 1,000 square meters of murals. Construction began in the Later Qin era (384-417 CE). #

Closer view of the Maijishan Grottoes in the city of Tianshui on August 12, 2015. The tallest statue is 16 meters tall and the smallest is only 10 centimeters tall. #

A train speeds through a gap in a section of the Great Wall of China, past Jiayuguan Pass, in front of the snow-covered Qilian Mountains in Jiayuguan, Gansu Province, on April 28, 2007. #

A farmer walks past a terrace of codonopsis pilosula, a traditional Chinese medicine also known as dang shen, in Min County, Gansu Province, on May 31, 2011. Rows of white plastic shields have been installed to protect the roots of the dang shen to keep it warm and moist. Commonly used as a cheaper substitute for ginseng, the herb is believed to lower blood pressure, boost the immune system, and improve appetite. #

Yueyaquan, or Crescent Lake, in Dunhuang, Gansu Province, on May 12, 2013. Formerly a silk route hub and center for trade between China and the West, Dunhuang relies heavily on tourism and features a number of historic sites dating back to the Han Dynasty. The city has an arid climate and is surrounded by sand dunes, a result of increasing desertification. #

Visitors walk on the Mingsha sand dunes on the outskirts of Dunhuang, Gansu Province, on April 29, 2007. According to local sources, the Mingsha sand dunes stretch more than 40 kilometers (25 miles) long and 20 kilometers (12.4 miles) wide, reaching heights of 1,715 meters (5,630 feet). #

A worker inspects solar panels at a solar farm in Dunhuang, Gansu Province, on September 16, 2013. China is pumping investment into wind power, which is more cost-competitive than solar energy and partly able to compete with coal and gas. #

A crumbling section of the Great Wall of China is seen near the rebuilt Jiayuguan fort, at rear, in China's Gansu province on October 11, 2005. Though parts of the Great Wall have been fully restored, much of it is in disrepair, with many areas crumbling or even buried under sand. #

A sandstorm hits the Shandan Horse Ranch in Zhangye, Gansu Province, on March 5, 2013. According to eyewitnesses, large amounts of black dust and sand were pushed by strong winds, resembling a wall rolling across the horse farm from the west. #

An aerial view shows people traveling along a road inside the Danxia National Geological Park, in Zhangye, Gansu Province, China, on July 5, 2015. The national geological park, covering an area of 510 square kilometers (197 square miles), is known for its colorful rock formations. #