Colter left Fort Raymond in October, 1807 with a pack weighing roughly thirty five pounds (not including his rifle and ammunition,) and traveled over five hundred miles 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 may have 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 .