One hundred years ago John Wesley Powell and nine adventure-seeking companions completed the first exploration of the dangerous and almost uncharted canyons of the Green and Colorado Rivers. By this trip, Powell, a 35-year old teacher of natural history, apparently unhampered by the lack of his right forearm (amputated after the Battle of Shiloh) opened up a large unknown part of continental United States and brought to a climax the era of western exploration.