[Seventh] Annual Report of the United States Geological and Geographical Survey of the Territories, embracing Colorado: being a report of progress of the exploration for the year 1873

In accordance with the recommendation of the Secretary of the Interior, an appropriation of $75,000 was made for the systematic survey of Colorado, and, at as early a date as the season would permit, the party reached Denver. This place formed our starting point for the various portions of the territory which had previously been marked out for the season's work. Early in the winter, the area to be surveyed in Colorado was divided into three districts, and a preliminary map was constructed, based on the land-surveys of the portions concerning which there was any definite knowledge. We found that none of the existing maps were of any great service in the more elevated portions of Colorado. The area to be surveyed comprised the eastern portion of the mountainous part of Colorado, and it was separated into three districts: North, Middle, and South districts.