The "Geological Exploration of the Fortieth Parallel" refers to a significant survey conducted in the mid-19th century along the 40th parallel north, which runs through parts of the United States. This exploration aimed to map the geological features and resources of the region, providing valuable information for future settlement and development. The survey was part of a broader effort to understand the American West's natural resources. Led by John Wesley Powell, the exploration included detailed studies of the Rocky Mountains and surrounding areas. The findings contributed to the knowledge of mineral deposits, water resources, and potential agricultural land, influencing westward expansion and economic growth in the United States.