A 6-cent stamp commemorating John Wesley Powell's geographic exploration of the Colorado River and Grand Canyon. "On May 24, 1869, 10 men in four boats embarked on a journey that covered almost 1,000 miles through uncharted canyons. Three months later only 6 of the company emerged from the depths of the Grand Canyon".
In 1871-72, Powell returned to lead a second expedition through Grand Canyon. This second expedition produced the first accurate maps and over 100 photographs."
Inception of the modern Colorado River: http://azgeology.azgs.arizona.edu/article/feature-article/2011/12/48-ma-...
