On May 31, 1805, Lewis and Clark proceeded their journey through the Missouri Breaks. Lewis wrote: βThe bluffs of the river rise to the hight of from 2 to 300 feet and in most places nearly perpendicular; they are formed of remarkable white sandstone which is sufficiently soft to give way readily to the impression of water; two or thre thin horizontal stratas of white free-stone, on which the rains or water make no impression, lie imbeded in these clifts of soft stone near the upper part of them; the earth on the top of these Clifts is a dark rich loam, which forming a graduly ascending plain extends back from 1β2 a mile to a mile where the hills commence and rise abruptly to a hight of about 300 feet more. The water in the course of time in decending from those hills and plains on either side of the river has trickled down the soft sand clifts and woarn it into a thousand grotesque figures.β