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The Geological Exploration of Arizona: The Role of State and Federal Surveys and the Geologic Map of Arizona

Article Author(s): 

Steve Reynolds
Jon Spencer
Stephen Richard
Phil Pearthree

Geologic Studies Between 1879 and 1924

Creation of the U.S. Geological Survey in 1879 resulted in greatly intensified study of the geology and mineral resources of Arizona. Much research was also carried out by scientists and engineers of the University of Arizona from 1891 onward. T. B. Comstock, first President of the University, wrote several articles on Arizona geology and emphasized, in 1895, the need for a geologic map of the territory. Arizona became a state in 1912 and the Arizona Bureau of Mines, predecessor to the Arizona Bureau of Geology and Mineral Technology and Arizona Geological Survey, was established in 1915, with offices at the University of Arizona. The Bureau and the U.S.G.S. jointly published the first "Geologic Map of the State of Arizona" in 1924.

A number of exceptional geologic studies were completed between 1879 and 1924. Many of their conclusions have been verified by 90 to 140 years of additional scientific research. The classic publications of F.L. Ransome, Waldemar Lindgren, N. H. Darton, and L. F. Noble are representative of this time period. Geologic studies of this era may be subdivided into four general types: 1) regional geologic reconnaissance; 2) geologic research on mineral deposits and their surrounding areas; 3) regional reconnaissance concerning water supplies; and 4) detailed research on rock units, minerals, and fossils. These four types of geologic studies are discussed in more detail below.

The first type, regional geologic reconnaissance, consisted of a more-or-less cursory examination of a large area. These studies included a variable amount of detailed investigation of the rocks and their relationship to mineral deposits and water resources. By necessity, the geologic maps produced by these pioneering regional geologists were quite generalized and thus subject to later refinements. However, these maps were the first all-important step toward accurately depicting the geology of the state. Such reconnaissance maps formed the basis for the first state geologic map.

An excellent example of this type of regional study is N. H. Darton's 1910 reconnaissance of northern Arizona and northwestern New Mexico. Darton's report contains a geologic map of a 100-mile-wide strip of land from Albuquerque to Kingman. It is in this report that Darton (1910) first proposed the names Kaibab limestone, Coconino Sandstone, and Supai Formation for the upper rock layers of the Grand Canyon. These names have been used by geologists ever since. Northern Arizona was the site of two other regional geologic studies during this period. H. H. Robinson mapped and described the geology of the San Francisco Mountains, focusing on the abundant volcanic features. The three periods of volcanism recognized by Robinson (1913) are still discussed today. Robinson spent much time pondering whether the volcanic field was extinct or simply dormant, but it is almost certainly dormant and will likely erupt many more times. East of the San Francisco Mountains, H. E. Gregory was investigating the regional geology of northeastern Arizona. Gregory (1917) describes the countryside as having few roads, virtually no satisfactory maps, only minor amounts of safe water, and an unfriendly Indian population. He goes on to state (p. 9): "Geological field work in such a country is necessarily reconnaissance; some of it, in fact, is exploratory."

The second type of geologic study was concerned with mineral deposits and their surroundings. These studies generally included detailed mapping of the surface and subsurface geology of the individual mines or mining districts. In several notable cases, the region surrounding the mines was also mapped in relative detail. F. L. Ransome's geologic maps of areas around Globe, Ray, Bisbee, and Oatman have remained untarnished by 100 years of additional research. In addition, many geological formations originally named by Ransome (1903, 1904) are still widely recognized. For example, Ransome named the Pinal Schist, Apache Group and Bolsa Quartzite, rock units that are familiar to most Arizona geologists. A contemporary of Ransome was Waldemar Lindgren, a famous economic geologist. Lindgren's 1905 geologic map of the Clifton-Morenci area has likewise survived years of scrutiny. Ransome's and Lindgren's maps were incorporated, virtually without modification, into both the 1924 and 1969 state geologic maps.

The third type of geologic study examined the relationship between regional geology and water supplies. The resulting reports generally described in detail the locations of watering holes, but were less concerned with the geology. In those days, water was a more immediate concern than rocks. Good examples of this type of study are the publications of W. T. Lee (1905, 1908), C. P. Ross (1923), and H. E. Gregory (1916). Lee (1908) examined the water resources of northwestern Arizona and summarized his findings as follows: "Conditions were found so unfavorable for water development in this region that the economic results of the work are unimportant, or at best have negative value." Lee would be greatly surprised by the large metropolitan areas of modern-day Phoenix and Tucson.

One of the more interesting water-related studies was Kirk Bryan's 1925 report on the geology and water supplies of the "Papago country" of southern Arizona. In addition to geology, Bryan's report contains excellent descriptions of the landscape, vegetation, and wildlife. Bryan refers to the Gila Monster as "a big clumsy lizard ... [that is] sluggish and difficult to annoy but has a brutish temper and a grip like a bulldog." He describes the pack rat as a "bold marauder in camps" that will carry off anything that is loose, returning with "rubbish of various kinds which he leaves in place of the pilfered articles, hence one of his names is 'trade rat." Bryan discusses kangaroo rats in the following manner (p. 51):

... several [kangaroo rats] came into camp which was lighted by a large fire. In spite of being shot at several times they persisted in coming back, and one was finally caught in the hand. The fore limbs are much smaller than the hind limbs, but are doubtless used more in walking than one would judge by the tracks. Certainly these individuals, when investigating the Survey camp, went on all fours.

The fourth type of geologic study was the detailed description and analysis of rocks, minerals, and fossils. C. D. Walcott's research in the Grand Canyon from 1880 to 1895 is exemplary of this type of detailed study. Walcott published a number of articles discussing the rock units and fossils of the canyon. Several important rock units in the canyon are still recognized by names that were originally proposed by Walcott.

Senior Geologist
Arizona Geological Survey


Research Geologist
Arizona Geological Survey

Steve Reynolds

Arizona State University School of Earth and Space Exploration

Steve Richard

Research Geologist
Arizona Geological Survey

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