An hundred miles above this, I passed a curious feature, called the “Square Hills” (+plate+ 123). I landed my canoe, and went ashore, and to their tops, to examine them. Though they appeared to be near the river, I found it half a day’s journey to travel to and from them; they being several miles from the river. On ascending them I found them to be two or three hundred feet high, and rising on their sides at an angle of 45 degrees; and on their tops, in some places, for half a mile in length, perfectly level, with a green turf, and corresponding exactly with the tabular hills spoken of above the Mandans, in +plate 39, Vol. I.+ I therein said, that I should visit these hills on my way down the river; and I am fully convinced, from close examination, that they are a part of the same original superstratum, which I therein described, though seven or eight hundred miles separated from them. They agree exactly in character, and also in the materials of which they are composed; and I believe, that some unaccountable gorge of waters has swept away the intervening earth, leaving these solitary and isolated, though incontrovertible evidences, that the summit level of all this great valley has at one time been where the level surface of these hills now is, two or three hundred feet above what is now generally denominated the summit level. The mouth of the Platte (+plate+ 124), is a beautiful scene, and no doubt will be the site of a large and flourishing town, soon after Indian titles shall have been extinguished to the lands in these regions, which will be done within a very few years. The Platte is a long and powerful stream, pouring in from the Rocky Mountains and joining with the Missouri at this place.