Published by the National Academy of Sciences, this biography of S. F. Emmons includes details on his activities in Colorado and elsewhere in the US West. Digital PDF download. GEO-1912-01D
The exploration as originally planned by Mr. King, modified by later experience and needs of the country, called for a survey of an area stretching from the Great Plains of Wyoming and Colorado over the Rocky Mountains, across the Salt Lake region and the desert valleys of Nevada, westward to the eastern boundary of California, determined by the 120th meridian from Greenwich. The proposed route of the first transcontinental railway was always included within the territory examined. This comprehensive plan called for a topographical map 100 miles in width, on a scale of 4 miles to the inch, based upon a system of primary and secondary triangulations, the elevations to be determined by a series of careful and frequent barometric readings, referred to a well-established main camp and checked by instrumental readings, by the railway from ocean level, across the Sierras, and thence along the Humboldt River. On these topographic maps geology was to be laid down. It should be borne in mind that such finished maps were seldom in the hands of the geologists till a year after completion of field work.