into the Sunlight Basin of modern-day Wyoming, which would make him the first known white man to have ever entered this region. Colter headed back toward civilization in 1807 and was near the mouth of the Platte River when he encountered Manuel Lisa, a founder of the Missouri Fur Trading Company, who was leading a party that included several former members of the Lewis and Clark Expedition, towards the Rocky Mountains. Among the band were George Drouillard, John Potts, and Peter Weiser. Colter once again decided to return to the wilderness, even though he was only a week from reaching St. Louis. At the confluence of the Yellowstone and Bighorn Rivers, Colter helped build Fort Raymond and was later sent by Lisa to search out the Crow Indian tribe to investigate the opportunities of establishing trade with them. Yellowstone, Grand Teton and Jackson Hole Colter left Fort Raymond in October 1807 and traveled over to establish trade with the Crow nation. Over the course of the winter, he explored the region that later became Yellowstone and Grand Teton National Parks. Colter reportedly visited at least one geyser basin, though it is now believed that he most likely was near present-day Cody, Wyoming, which at that time may have had some geothermal activity to the immediate west. Colter probably passed along portions of the shores of Jackson Lake after crossing the Continental Divide near Togwotee Pass or more likely, Union Pass in the northern Wind River Range. Colter then explored Jackson Hole below the Teton Range, later crossing Teton Pass into Pierre's Hole, known today as the Teton Basin in the state of Idaho. After heading north and then east, he is believed to have encountered Yellowstone Lake, another location in which he had seen geysers and other geothermal features. Colter then proceeded back to Fort Raymond, arriving in March or April 1808. Not only had Colter traveled hundreds of miles, much of the time unguided, he did so in the dead of winter, in a region in which nighttime temperatures in January are routinely . Colter arrived back at Fort Raymond, and few believed his reports of geysers, bubbling mudpots and steaming pools of water. His reports of these features were often ridiculed at first, and the region was somewhat jokingly referred to as "Colter's Hell". The area Colter described is now widely believed to be immediately west of Cody,