The dusty landscape of the American West is dotted with enormous concrete arrows. They look like cryptic messages from a primitive civilization — a civilization that was obsessed with westward expansion. And that assessment wouldn't be altogether wrong. But these enormous arrows pointing west tell only part of the story. Because at the dawn of aviation, they were part of America's highway of light — a high-tech system of lighthouses showing pilots how to get from New York City all the way to San Francisco.