While exploring with the Wheeler Surveys in 1871 and 1872, Grove Karl Gilbert recognized and demonstrated that faulting, rather than folding, dominated mountain building in the basin ranges. Widely accepted now, this concept was challenged by Spurr and others. Gilbert recognized further that relief had been produced incrementally along these range-bounding faults, evidenced by “piedmont scarps,” which he first noted and named. Piedmont scarps, in turn, he recognized as evidence of earthquakes, and in 1883 he warned the citizens of Utah that the absence of such scarps along one segment of the front of the Wasatch Range strongly suggested that a large earthquake might eventually occur there. That warning was the first paper on earthquakes authored by a member of the fledgling U.S. Geological Survey.

Gilbert’s studies of the San Francisco earthquake of 1906 stand out to present-day investigators as his principal contribution to the knowledge of earthquakes. His photographs, diagrams, and descriptions of the behavior of the San Andreas fault during that earthquake are data that have been used repeatedly during the 1960s and 1970s. But almost unknown to investigators during those decades was Gilbert’s paper “Earthquake Forecasting,” published in 1909. It was the only paper listed in the Bibliography of North American Geology between 1785 and 1922 about earthquake forecasting or predictions. The issues and concepts in Gilbert’s paper—earthquake prediction, earthquake engineering, land use, risk evaluation, and insurance—anticipated many elements of the Earthquake Hazard Reduction Act of 1977.

It was not the quality or originality of a particular work of Gilbert that governed its impact on subsequent studies, but rather the existence or nonexistence of a scientific audience, suitably attuned to the subject at hand and sufficiently knowledgeable to perceive and be influenced by his work.