Gilbert’s studies of underground water were overshadowed by his magnificent reports on geologic structure and landforms. In fact, his 1896 publication on the underground water of the Arkansas Valley in eastern Colorado was called by W. M. Davis “for the most part a straightforward geological account of the successive strata.”

Gilbert’s 1896 report devoted equal space to stratigraphy and to underground water. His discussion of artesian water was based largely on Chamberlin’s excellent paper on that subject, a decade previously; he briefly acknowledged his debt to Chamberlin for the section dealing with the general occurrence of artesian water, and acknowledged more completely his debt to his U.S. Geological Survey colleague, F. H. Newell.

Gilbert’s reports of 1896 and 1897 are largely practical ones on where and how to explore for artesian water, and they include maps showing areas where water can be expected in wells at different depths. Plagued by too little information, he was courageous enough to put lines on a map, although he admitted that the data “are too imperfect to fix the lines definitely except at a few points.” Thus, he said, “I confess that I have drawn this map with much reluctance.” He recommended experimental borings, to gather the additional information needed before putting down a well.

Gilbert intended his text and maps to be read by local residents (nongeologists) in their search for artesian water supplies, and this is seen as a major contribution of his work on the underground water of the Arkansas Valley.