context: Rocky Mountains () is a vast mountain range in western North America. It stretches 4800 kilometers from Mexico through the United States to Canada. It belongs to the so-called "young corrugated mountains," created during the last 60 million years when lithospheric tiles collide. The highest peak of the Rocky Mountains on the US side is Mount Elbert in Colorado. It is 4399 meters high. In Canada, its highest peak is Mount Robson, which reaches 3,959 meters.
question: How were the Rockies born?
answers.text: lithospheric tiles collide