T50 Geology in the National Parks; Research, Mapping, Education, and Interpretation

Monday, 5 November 2001
1:30 PM - 5:30 PM

GEOLOGY OF CITY OF ROCKS NATIONAL RESERVE: NEW INSIGHTS FROM KECK GEOLOGY CONSORTIUM UNDERGRADUATE RESEARCH

Paper number: T50-9
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The City of Rocks National Reserve encompasses a scenic landscape of fins, spires, and domes eroded from the Oligocene Almo Pluton and the Archean Green Creek Complex in the core of the Albion Range metamorphic core complex. The "Silent" City of Rocks was a landmark on the California Trail that was often mentioned in the diaries of the forty-niners. Recent human history has been the focus Cof most of the interpretive resources of the National Reserve in spite of its fascinating geologic history. In the summer of 2000, a Keck Undergraduate Research Project was conducted in an effort to better understand the processes and geologic controls that created the spectacular landscape and to communicate these concepts to park staff. Individual student projects addressed geologic problems that are often the source of visitors’ questions. The results of the projects were made available to park staff, and a route for a geologic interpretive trail was laid out.

The primary results of the student projects can be summarized as follows: Joint sets in the City of Rocks are the most important factor in controlling the spacing, shape, and distribution of rock outcrops. Individual joint sets can be tied to discrete tectonic events. For example, a north-striking joint set related to Oligocene extension hosts hydrothermal alteration and mineralization and is responsible for the formation of the major "avenues" of the City of Rocks. Panholes have played a very important role in shaping and lowering the surfaces of rock outcrops; their shape and size evolves through time in a predictable manner. Flare structures along the bases of outcrops are not randomly distributed but can be related to parameters such as aspect, slope, and soil moisture. The Circle Creek Basin which contains the City of Rocks appears to have developed through discrete stages of relative stability separated by periods when the erosion of deeply weathered granite was accelerated as a result climatic changes, tectonic uplift, or both.