1911 Encyclopædia Britannica, Volume 19… (1911)
“ Being remarkably free from trees, rocks and streams, the soil can be turned in furrows that run perfectly straight for miles, and favours the development of “bonanza farms,” where thousands of acres are cultivated in a single field. The soils W. of the valley consist of glacial drift, and are well suited to the growing of grain. The drift becomes thinner toward the W., and finally disappears in the semi-arid regions of the Missouri river valley. In this region the soils of sand and clay are much finer than the drift, and are very productive where the water-supply is sufficient. ”
