In 1846, at the insistence of President James K. Polk, First Lieutenant William H. Emory led a military reconnaissance across the southwestern USA. The journey started in Missouri and ended in San Diego, California. Emory described the dramatic Basin and Range topography thus: “The mountains run from northwest to southeast, and rise abruptly from the plains in long narrow ridges, resembling trap dykes on a grand scale” (cited in A. M. C. Sengor, 2003, Geological Society of America Memoir 196, Boulder, CO, p. 170). Emory's detailed report to the U.S. Congress was published in 1848 and was followed by many...

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