Pierre Antoine and Paul Mallet

Pierre Antoine and Paul Mallet, brothers and French Canadian voyageurs, were the first Europeans known to have crossed the Great Plains from east to west. They first journeyed to Santa Fe, New Mexico from Kaskaskia, Illinois in 1739.

Pierre Antoine Mallet (b. 20 June 1700, d. after 1750) and his brother Paul Mallet (b. ?, d. 1753, Arkansas Post, Arkansas), were born in Montreal, Canada and moved to Detroit in 1706 and Kaskaskia, Illinois in 1734. From Kaskaskia, in 1739, they attempted to travel to Santa Fe, New Mexico with six companions and nine horses loaded with trade goods. They followed the Missouri River north to South Dakota to the villages of the Arikara. It was believed at the time that the Missouri River flowed all the way to the Spanish colonies in New Mexico. Told by the Indians that New Mexico was to the southwest, they backtracked to the Pawnee villages on the Loup River in Nebraska. From there on May 29, 1739, they embarked for Santa Fe.

The Mallet’s account of their journey to Santa Fe was lost and their route can only be roughly approximated. They followed the Platte and South Platte River, which they called the River of the Padoucas (Padoucas probably refers to the Apache Indians who had inhabited this area a few years earlier). They followed the South Platte upstream to approximately the Colorado-Nebraska border, then turned south. While crossing a river (probably the Republican), they lost seven horses loaded with merchandise. They reached the Arkansas River near the Kansas-Colorado line and followed it upstream.

...
Wikipedia