Detailed geologic maps are one of the most important tools available to geologists for determining tectonic history. This report is essentially a critique of selected maps (fig. 1), most of which have been published since 1958 when currently accepted concepts of the tectonic history of the region were first formulated by R.J. Roberts and others. The purpose of this report is to highlight the most significant stratigraphic and structural relations displayed on these geologic maps, stressing the significance of the maps individually and collectively for the tectonic history of the region. The age ranges of several stratigraphic units shown on many of the maps are no longer valid, and the maps are unlikely to be revised in the near future. Accumulating paleontological data has led to improved stratigraphic concepts and therefore made possible an improved understanding of the tectonic history. A principal aim of this report is to make the revised ages of stratigraphic units more widely known. Existing maps represent tremendous physical and mental effort by geologists over the last four or five decades, but unfortunately, the tectonic interpretations in many cases seem to have been driven more by ideology than by the observed structural relations. As a result, interpretations are commonly at variance with the map evidence as noted in the following pages. This report necessarily demands much from the reader. For maximum benefit from the discussions that follow, the reader should examine the principal geologic maps to which reference is made. Brief summaries of pertinent aspects of stratigraphy and structure are presented, but to duplicate herein parts of the many geologic maps to which reference is made, or to describe in detail the stratigraphy and structure of each map area, would be impractical. Simplified sketches of the maps would be useless; the message is in the details.

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For more information about this report contact: Keith B. Ketner

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