The city of Timbuktu has long had a reputation for being a distant and even mythical place. Given its strategic location at the edge of the Sahara Desert and the Sahel, the city was once a center of scholarship and a key hub along salt, gold, and ivory trading routes.

In the modern era, Timbuktu is a modest city of 50,000 people in central Mali, and the main industries are agriculture and tourism. Still, getting there remains a challenge. Flights in and out are scarce, and boats can only travel up the Niger River when water levels are high. The red roads that link the city to other population centers to the southeast and south may be the most reliable way to reach the city.

As shown by this natural-color Landsat image, the red of the roads contrasts sharply with the lighter-colored sands common in the Sahara Desert. The roads are likely made of laterite, an iron- and aluminum-rich soil and rock type common in southern Mali. Long exposure to air and water turns laterite red as it becomes rich in hematite.

“Laterite is one of the least soluble materials known to man and so is left behind after millions of years of leaching of the soils by rainfall,” explained Earle Williams, an earth scientist at the Massachusetts Institute of Technology.

While laterite is an abundant and widely used road-making material in Mali, it does pose some challenges. If unpaved, it can turn to mud in the wet season and make travel slow. And during the dry season, vehicles can kick up large amount of dust from unpaved laterite roads.

NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.