The desperate search for two people who disappeared at the bottom of the Grand Canyon last weekend marked the National Park Service's most extensive use yet of drones for a search-and-rescue operation.
The Grand Canyon is the only national park to have its own fleet of unmanned aircraft for finding people. It has five drones, capable of peering into crevices and other places unreachable on foot.
Operating drones is also considered safer than sending rangers up in helicopters.
Still, the drones were unable to find the woman and teenage boy who vanished while crossing a creek, and the search has been scaled back.