The following data is extracted from Days of Yore: Early History of Brown County, Nebraska.
Sheldon's History of Nebraska gives this interesting account of the explorations by the Spaniards. One expedition led by a Scotchman, James Mackey, (Fr. Jacques Machey) reached the region of the North Loup River in 1795-96. He continued westward to the great Sandhill lakes of Cherry County, then traveleled northward to the Niobrara River which he followed down to where it joins the Missouri river. Mackey made an accurate map of the regions that he had explored which was published in Paris in 1802. On this map in the region of Long Pine creek is this inscription: "Mountains of sand, underlain by subterranean and invisible streams in the midst of which is a great canyon, two hundred fifty feet across and one hundred fifty deep, formed by the washing of the mountains." This map entitles Mackey to the honor of being the first white man to explore the sand hill region of Nebraska. If others came they left no record of having visited this locality.
These early explorers were followed by men in search of new homes. Settlements were made along the Missouri River, and from these settlements the more venturesome ones followed up the rivers that empty into the Missouri for the purpose of hunting and trapping wild animals for food and furs. These were taken back to the settlements and traded, bringing good profits to, the hunters. It took only a few years of this systematic hunting to kill off the immense herds of buffaloes. They were slaughtered without mercy, the white hunters taking only the hides and the choicest cuts of meat. With the vanishing of these animals the main source of food was taken from the Indians, and they became very hostile to all white men who ventured to cross the borders into their hunting grounds.
The discovery of gold and silver in California and other western states lured thousands of men from eastern states to try to reach the gold fields where they hoped to become rich by their findings. It is possible that some of these gold seekers may have crossed our country.
Missionaries were sent to the Indian tribes in the hope that they might be taught the principles of the. Christian faith and the ways of civilized living. These devoted men came from the white settlements along the Missouri river or from their homes in the eastern states. All of these venturesome men, whatever their purpose in coming-the early explorers, the hunters of wild game, the gold seekers and the devout missionaries, left slight traces of their travels. A trail through the tall grass, ruts made by wagon wheels, ashes left from a campfire, all told a story to the white men who came later.
In time these dim traces of travel were a followed by other men making a well marked route, known by a name to direct other travellers. Slight traces of these old trails may still be seen in places. The earliest of these is probably the "Sawyers Trail." It was begun in 1865 by a United States government expedition for the use of freighters taking supplies and mining machinery to Virginia City, Montana, where gold had been discovered. Its eastern terminus was Niobrara (at the mouth of the Niobrara River) and passed across Brown County a few miles south of that river.
Source: Days of Yore: Early History of Brown County, Nebraska