The famous Hayden Expedition of 1871, led by geologist Ferdinand V. Hayden, was instrumental in surveying and mapping what would become Yellowstone National Park the following year. The survey expedition, which took about four months over the summer of 1871, was funded by Congress. Six years later, in 1877, Hayden and his team surveyed Colorado and Utah. The Colorado Geological Survey has digitized several of Hayden’s geologic maps from the 1877 expedition, which you can find online by clicking here. Hayden’s maps are an important part of the study of the geology of the West, and the town of Hayden in western Colorado’s Yampa Valley has been named for him.