||VEGETATION, SOIL AND WATER 23 Soil Erosion The first step in the solution of our soil problems is a public enlightenment of the facts of soil erosion and what these facts mean to every citizen of the state, urban as well as rural. A special survey in the Sevier Lake watershed of south-central Utah* revealed that serious soil losses have occurred on all but about one-fourth of the 4.8 million acres of mountainous lands in that drainage basin since settlement. The enormity of this loss can be realized only if we understand the rate of soil formation and the dependence of our multiple use of the land on these precious few inches of the soil mantle. The history of soil always starts with rock weathering and the beginning of vegetation on rock material. The character of any particular soil depends on many factors, chief of which are the basic rock materials and the climate under which soil is formed. Utah with its diversity of climates therefore presents a great diversity of soils. But all soils after countless eons of time develop certain qualitative similarities in that the top few inches contain most of the organic matter and the available mineral elements necessary for the support of vegetation. The rate of soil formation of course varies with the climate and the nature of the substratum from which it is formed, but Bennett4 says: "Soil is reproduced from its parent material so slowly that we may as well accept as a fact that, once the surface layer is washed off, land so> affected is, from the practical standpoint, generally in' a condition of permanent impoverish" ment. As nearly as can be ascertained, it takes nature under the most favorable conditions, including a good cover of trees, grass, or other protective vegetation, anywhere from 300 to 1,000 years or more to build a single inch of top soil. When seven inches of top soil are allowed to wash away, therefore, at least 2,000 to 7,000 years of Nature's work goes to waste." We are living on a dynamic earth. Erosive forces have always been at work. Just as surely as mountains arise, the forces of rain, wind, frost, ice and chemical reactions will slowly but surely reduce them to level plains. As Tennyson says in his "In Memoriam": "The hills are shadows, and they flow From form to form, and nothing stands; They melt like mist, the solid lands, Like clouds they shape themselves and go." But these infinite grinding processes by the mills of time known as "normal" or "geologic" weathering must be carefully distinguished from accelerated erosion that can remove many inches of top soil from watershed slopes. Indeed during a storm on August 19, 1945, that caused $345,000 flood damage to Salt Lake City, some of the flood-producing watershed lands lost up to ten inches of soil in less than one hour. * Flood Control Survey Report, Sevier Lake Watershed. Incomplete draft on file, Intel-mountain Forest and Range Experiment Station, Ogden, Utah.