ABSTRACT: Hydrogeology is concerned largely with ground water and, as ground water occurs in a geologic environment, an understanding of the geologic fabric and framework is essential to its development and use. But ground‐water flow, discharge, recharge, response to pumping and other related matters, including salt‐water encroachment, are described by mathematical formulas and tested by engineering techniques. Until both the sciences of geology and engineering hydrology were far enough advanced to be of practical help, in the late 1800's, hydrogeologic progress was stymied. Additionally, an economic need for hydrogeologists was required before a demand developed for such scientists. With the opening of the West in the late 1860's the demand came. Hydrogeologists were needed to find irrigation water for the arid lands. Concomitantly, in the South, ground water was needed for growing rice, corn, and cotton. The rapid growth of cities, especially in the North, required hydrogeologists to find safe supplies of clean, pure water to replace polluted surface‐water sources. By the early 1900's engineering techniques and equipment needed to drill and pump the deep wells and to evaluate the aquifer pumping tests were available, satisfactory for the times, but clumsy and awkward by modern standards. By 1912, the beginning of the “Meinzer Era,” the U.S. Geological Survey had developed into the foremost governmental scientific organization in the world and its small cadre of hydrogeologists were world leaders in their science. A wealth of information concerning the history and development of the science was summarized by Meinzer (1934). Oscar E. Meinzer, regarded as the Father of Hydrogeology in America, was the third Chief of the Ground‐Water Branch (1912–1946) (Figure 1).