During his expeditions and explorations of the Rocky Mountains, Campbell wrote a series of letters to his brother between the years 1832 and 1836 which were published in a Philadelphia newspaper titled The National Atlas and Tuesday Morning Mail in a series of issues numbering 14-19, Nov 1 - Dec 6, 1836. These letters described his travels in the Rockies, the appearances and customs of the Natives he became acquainted with and even the deaths of some comrades. The letters were first reprinted in 1955 as The Rocky Mountain letters of Robert Campbell for Frederick W. Beinecke.