Which factor helped to form the Atacama Desert?

Explanation: This mix of mountains, winds, and ocean currents combines to make the Atacama incredibly dry. The Atacama is also one of the oldest deserts in the world. Scientists think parts of it have been dry for at least 20 million years and maybe as long as 40 million years. That is much older than other very dry desert

 this desert is located in the "rain shadow" between two mountain ranges, the Andes and the Chilean Coast Range. Second, winds called the Pacific Anticyclone flow through this area. Those winds blow dry air into the Atacama Desert.