The alkali lakes of Nebraska are believed to be of very recent geologic origin. They lie in depressions in a former sand dune area, and contain large quantities of potash supposedly accumulated by leaching of the ashes resulting from repeated burnings of the grass in the adjacent country.
Of other natural mineral sources, alunite is the most important. The principal deposits worked are at Marysville, Utah, but the mineral is a rather common one in the western part of the United States, associated with gold deposits, as at Goldfield, Nevada. Alunite occurs as veins and replacement deposits, often in igneous associations, and is supposed to be of igneous source. Its origin is referred to in connection with the Goldfield ores (p. 230).
FOOTNOTES:
[15] Gale, Hoyt S., The potash deposits of Alsace: Bull. 715-B, U. S. Geol. Survey, 1920, pp. 17-55.
[16] Gale, Hoyt S., Potash deposits in Spain: Bull. 715-A, U. S. Geol. Survey, 1920, pp. 1-16.