Powell retraced part of the 1869 route in 1871–1872 with another expedition that traveled the Colorado River from Green River, Wyoming to Kanab Creek in the Grand Canyon. This trip resulted in photographs (by John K. Hillers), an accurate map and various papers. At least one Powell scholar, Otis R. Marston, noted the maps produced from the survey were impressionistic rather than precise. In planning this expedition, he employed the services of Jacob Hamblin, a Mormon missionary in southern Utah and northern Arizona, who had cultivated excellent relationships with Native Americans. Before setting out, Powell used Hamblin as a negotiator to ensure the safety of his expedition from local Indian groups.