Almon Harris Thompson (September 24, 1839 – July 31, 1906), also known as A. H. Thompson, was an American topographer, geologist, explorer, educator and Civil War veteran. Often called "The Professor" or simply "Prof", Thompson is perhaps best known for being second in command of John Wesley Powell's Second Geographical Expedition (1871–1875), a federally funded scientific expedition that retraced the route of Powell's original expedition in order to further explore and map the drainages and canyons of the Green and Colorado Rivers in what is now southern Utah and northern Arizona. Thompson's diary of the expedition was originally published in the Utah Historical Quarterly in 1939. Through his work on the Powell expeditions and later as a geographer at the U.S. Geological Survey, he was re