Ferdinand Vandiveer Hayden (1829-1887), American geologist. Hayden initially trained as a doctor, but became interested in geology after a fossil- collecting trip to South Dakota, USA. He was head of the US Geological Survey of the Territories between 1867 and 1879, which focused on Nebraska, Wyoming, Colorado and Idaho. His work led to the establishment of the Yellowstone National Park in Wyoming in 1872. Hayden was friends with the influential palaeontologist Joseph Leidy, with whom he collaborated several times. Leidy helped to secure Hayden an associate professorship at the University of Pennsylvania.