Geological Survey Professional Paper 669 The Colorado River Region and John Wesley Powell

During the first third of the present century, studies involving the stratified rocks of Grand Canyon greatly increased, and many new geologists appeared on the scene. Probably some of the acceleration in geological activity was directly related to opening of the Bright Angel and El Tovar Hotels in 1896 and 1905, respectively, and to the construction of a branch line of the Santa Fe Railroad to the South Rim in 1901. This made the Grand Canyon much more accessible than before. Also, a general increase in the number of geologists and the spreading fame of the Grand Canyon probably contributed to an expansion of interest.

Many of the studies during this period were of local areas, were limited in scope, and merely added to the sum total of general knowledge. Among the contributors were such eminent geologists as F. L. Ransome (1908, 1916), N. H. Darton (1910, 1925), H. H. Robinson (1913), Charles Schuchert (1918a, 1918b), J. B. Reeside, Jr., and Harvey Bassler (1922), R. C. Moore (1925), and C. R. Longwell (1928). New descriptive data and, in some cases, detailed sections for various rock formations were recorded. Ideas concerning paleogeography, especially the probable locations of positive elements in neighboring regions, and the sources of sediments were suggested by Ransome (1916), Schuchert (1918a), and Darton (1925). Many paleontological papers by C. D. Walcott (1897-1925) were published, although his Grand Canyon fieldwork had been finished before 1900. Many Cambrian fossils from Grand Canyon were described by him, and one paper (Walcott, 1918) was devoted to the tracks and trails of trilobites and other invertebrates. Other trace fossils, consisting of reptilian footprints in the Permian Coconino Sandstone and probable amphibian tracks in the Supai Formation of Pennsylvanian and Permian age, were studied by Gilmore (1926, 1927, 1928).

Some new formation names were given and some type sections were selected during this period, and terminology was being stabilized. The names Supai Formation, Coconino Sandstone, and Kaibab Limestone were proposed by Darton (1910, p. 25-28) for units of the Aubrey Group. Likewise, Tapeats Sandstone, Bright Angel Shale, and Muav Limestone were proposed by Noble (1914, p. 41, 61) for divisions of the Tonto Group; Hotauta Conglomerate, Bass Limestone, Hakatai Shale, Shinumo Quartzite, and Dox Sandstone were proposed for units in the Unkar Group. (Noble, 1914, p. 41). A new formation, the Hermit Shale, was created from the upper part of the Supai (Noble, 1922, p. 64). Thus, most of the Grand Canyon formations as we know them today had been recognized and named by 1935.

The contributions of one geologist—Levi Noble—during the period 1900 to 1935 were outstanding. A very large fund of factual data, which has stood the test of subsequent checks was accumulated by Noble; furthermore, he attempted a considerable amount of thought-provoking interpretation. Like Newberry in the earliest days and Walcott somewhat later, he advanced ideas, using all the evidence at hand, to interpret the genesis of the various stratified rocks and to explain the missing intervals. Perhaps the most important feature of Noble's work, however, was the pattern of stratigraphic study that he promoted and that has strongly guided much subsequent investigation in the region.

Noble (1914, p. 60) recognized that although "the distribution and broader character of the [stratified] rocks of the Grand Canyon are familiar to every geologist * * *," details of stratigraphy were still very imperfectly known. He stated (p. 60) that "a close and accurate comparison and correlation of the thickness and character of the Paleozoic formations from place to place in the Grand Canyon must therefore depend on the results of future detailed work at many points." Noble (1922) then proceeded to follow his own advice; he produced a classic paper on detailed stratigraphy in which trends and changes in all Paleozoic formations of eastern Grand Canyon were described and analyzed for a distance of about 30 miles. This work set the stage for most subsequent studies, especially those involving paleogeography, the distribution of life, environment of deposition, paleoclimate, and other interpretive subjects.

One of the earliest attempts to analyze in detail available data bearing on the environment and history of the entire sequence of stratified rocks in Grand Canyon was presented by Noble (1914, p. 80-88). In his synthesis, he described his concepts of the genesis of each successive formation from bottom to top of the canyon walls and discussed for each unit such features as climate, advances and retreats of the sea, agents of sediment transport, and sources of sediment. An excellent illustration of Noble's (1914, p. 62) skill in describing and interpreting environmental features is seen in the following quotation:

Within the Tapeats sandstone is a record of marine planation that in these vertical sections, which include no soil, is preserved with a clearness that is almost beyond belief. The long southwestern face of the Unkar island monadnock was undercut by the waves of the sea in which the sandstone was deposited, and a cross section of this old sea cliff preserved in the Tapeats sandstone in the southern wall of Hotauta Canyon near the Colorado reveals clearly every detail of the structure; at the base of the cliff huge angular blocks of Shinumo quartzite are incorporated in the Tapeats sandstone in the places where they fell and lodged; farther out lie masses of bowlders, worn and rounded by the pounding of the waves; and these bowlders run into lenses of fine pebbly conglomerate, representing the shingle of the ancient beach, dragged out by the undertow. No more striking example of a fossil sea cliff can be imagined.