On the 22d of May, 1842, Lieutenant John C. Fremont, of the United States Corps of Army Engineers, arrived at St. Louis in pursuance of orders from the War Department, to command an exploring expedition westward to the Wind River Mountains. On the 10th of June he started with the celebrated Kit Carson as his chief guide; his route was up the Kansas River to the Blue, thence across to the Platte, which he reached on the 25th. The principal object of his expedition was a survey of the North Fork of that river. He found the width of the stream, immediately below the junction of its two principal branches, to be 5350 feet. Hunting buffalo and an occasional Indian scare were the only important incidents of his march up the valley. The expedition returned by the same route and arrived at the mouth of the Platte on the 1st of October.
Before reaching Laramie’s Fork, he met on the 28th of June a party of fourteen trappers, in the employ of the American Fur Company, making their way on foot with their blankets and light camp equipage on their backs. Two months previously they had started from the mouth of the Laramie River in boats loaded with furs destined for the St. Louis market. They had taken advantage of the June freshet, and were rapidly carried down as far as Scott’s Bluffs. There the water spread out into the valley, and the stream was so shallow they were compelled to unload the principal part of their cargo. This they secured as well as possible, and left a few of their men to guard it. They continued struggling on with their boats in the sand and mud fifteen or twenty days longer, then, farther progress being impossible, they cached their remaining furs and property in trees on the bank of the river, and, each man carrying what he could on his back, started on foot for St. Louis. The party was entirely out of tobacco when they were met by Fremont, who kindly gave them enough to last them on their homeward journey.
During the next decade the Platte Valley witnessed a wonderful change. From the habitat of the lonely trapper, hunting on its many streams, it became the chosen route of a vast migration, seeking possession of the virgin soil of far-off Oregon, or attracted by the discovery of gold in California. The hegira of the Mormons to the sequestered basin of the Great Salt Lake also swelled the stream, and was followed soon after by the establishment of the overland stage, the pony express, and the building of the Union Pacific Railroad.