The Red River continued to elude American exploration for another seventy years. The Long Expedition of 1819-1820 was to target the Red River. It set out from Council Bluffs, across the plains to Colorado, explored the Front Range of Colorado, and Stephen Long then followed the Rocky Mountain Front down into New Mexico, looking for a river exiting from the Southern Rockies, which he assumed would be the Red. They found such a river, began following it back east, and after about 350 miles it drained into the Arkansas. It turned out to be the Canadian.
And so the Long Expedition failed to find the headwaters of the Red River too. In 1852 the government sent Randolph Marcy into the southwest to try to find the headwaters of the Red River. He explored up the Red River and got to those canyon lands in the Texas Panhandle, ascended one of the really dramatic canyons there, which is called Tulé Canyon, proclaimed it to be the headwaters, and for about 25 years everyone assumed it was, until army commanders during the Indian wars in the 1870s began discovering more canyons, and more draws and streams farther west.
And so finally, in 1877, Congress sent out another expedition under a guy named Ernest Ruffner, who spend four months, and finally mapped the headwaters of the Red River. It was the last major river in the whole West to be explored. The Missouri and Columbia had long since been explored, the Colorado River had been explored, the Arkansas had been explored. The Red River's headwaters were finally discovered in the same decade that the headwaters of the Nile were found in Africa. It took till the 1870s.