Cyrus Thomas

[1] Four years later in 1869 he joined the expedition of Ferdinand Vandeveer Hayden, who had organized a science corps for the exploration of the Rocky Mountains.

In 1869 his professional scientific career began with his appointment as an assistant in entomology in the United States Geological and Geographical Survey of the Territories[1] under Professor Ferdinand Vandeveer Hayden.

Thomas was also the agricultural statistician and entomologist on the Hayden Geological Survey of 1871, whose work supported the creation of Yellowstone National Park in 1872.

[4] In 1873 Thomas was appointed a professor of natural science at Southern Illinois Normal University, which gave him a public forum for his ideas.

Thomas made some noteworthy contributions as an entomologist, having helped control the insect plague that was slowing the growth rate of the border states.

[6] With this information they were able to predict the outbreaks rather accurately for the upcoming year, and entomologists and farmers worked together for better times to plant and harvest.

By the end of his research into the origin of the mound builders Thomas dismissed each argument advanced in favor of the vanished race theory.

He was a leading proponent of the now-debunked theory known as "rain follows the plow", which stated that increased population and cultivation of the Great Plains would render the land lush and fertile.

This theory was used to promote expansion into the American West by persuading would-be settlers that the current lack of precipitation would not hinder their ability to engage in agriculture.