The Geology of Chaco Canyon, New Mexico In Relation To The Life And Remains Of The Prehistoric Peoples Of Pueblo Bonito Smithsonian Miscelleanous Collections Volume 122, Number 7

THE GEOLOGY OF CHACO CANYON
NEW MEXICO

IN RELATION TO THE LIFE AND REMAINS OF THE PREHISTORIC PEOPLES OF PUEBLO BONITO

By KIRK BRYAN¹

(WITH 11 PLATES)

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¹Dr. Bryan died on August 23, 1950.

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On the initiative of Neil M. Judd, leader of the National Geographic Society's Pueblo Bonito Expeditions, and on the recommendation of Dr. John C. Merriam, then president of the Carnegie Institution of Washington, the present writer was selected to undertake an inquiry into the geologic history of Chaco Canyon. Two brief periods were devoted to field work: July 28 to August 9, 1924, and July 10 to August 1, 1925. In the well-ordered camp of the expedition he was received with gracious hospitality, and to all members of the staff he owes much in kindness. Mr. Judd placed every facility at his disposal including a number of excavations especially designed to bring to light geologic facts and thus expedite the investigation.

Application of the stratigraphic methods of geology to archeological problems is no longer new, and knowledge of these methods forms a part of the equipment of every modern archeologist. Our inquiry into Chaco Canyon geology has proved (1) that the alluvial deposits of the canyon carry various relics of prehistoric peoples and (2) that the deposits can be separated into divisions of differing age. In recent years knowledge of these generalizations has become widespread and additional data have been gathered. It appears that we are now on the brink of establishing in the Southwest an alluvial chronology based on a sequence of episodes of erosion and alluviation. This sequence of geologic events gives a key to the fluctuations of climate of late geologic time and yields a proximate cause for the sudden decay of the great Pueblo communities of the San Juan country. (Bryan, 1941.)

Previous work on the general geology of this region is referred to hereinafter. During the summers of 1899 and 1901, Prof. Richard E. Dodge made a geological survey of Chaco Canyon as part of the extensive plans for the Hyde Exploring Expedition. His work was done after archeological excavation had ceased, and, unfortunately, his results were published only in skeleton outline in the report of the expedition (Pepper, 1920, pp. 23-25) and in three abstracts (Dodge, 1902a, 1902b, 1910). Even so, these brief sketches record a number of observations of interest that are referred to in the following pages. They indicate that Professor Dodge was on the verge of discovery and, with more archeological help, the geological theory herein set forth would doubtless have been advanced by him 20 years earlier. The 1877 observations of W. H. Jackson (1878) were keen and penetrating, and from exposures no longer visible he made the original discovery of the buried channel whose description and interpretation form such a large part of this report.

The long delay between initiation of this study and its publication has not been without advantage. During the interval we have learned that the geologic history of Chaco Canyon is not unique. Other valleys have similar histories, as will appear from the data on these other valleys summarized hereinafter. Generalizations on the cause of the alternations from erosion to alluviation and on the effect of these events on human affairs now rest upon a foundation of fact much larger than would have been possible in 1924 and 1925.