A History of South Dakota - From Earliest Times #229767

1. At the beginning the territory embraced within the present State of South Dakota, was deeply submerged under the primeval ocean. In the process of time, the internal forces of the earth threw up the Black Hills region, which through the course of countless years was exposed and submerged, again and again, until thousands of feet of the surface rocks had been broken up, reduced to sand and clay, and distributed over the ocean-bed of that portion of the present state extending as far east as the Missouri River.<br><br>2. The eastern portion of the state, too, had at different periods been exposed and submerged. Finally, however, the ocean drained away, leaving a gentle unbroken slope from the Black Hills down to the Missouri river, which at that period poured its irresistible flood, many times greater than at this time, down the present course of the James river. The Grand river continued its course east, emptying into the Missouri, near the present city of Aberdeen. The mouth of the Cheyenne river was near Huron, and the White found its way into the Missouri, not far from the city of Mitchell.<br><br>3. The climate was sub-tropical.