Detailed map of the area from Del Norte to Animas River, published by the the United States Geological Survey.
Place names shown include Silverton, Howardville (Howardsville), Mt. Sneffels, Uncompaghre Peak, Mt. Wilson, San Miguel Lake, Engineer Mountain, Pigeon's Peak, San Cristoval Lake, Mineral Point.
The Hayden Survey of Colorado
The late 1860s and early 1870s saw four great surveys of the American West: the King Survey, which mapped the region around the 40th parallel; the Wheeler Survey, which attempted (unsuccessfully) to map the whole of the territories and western states at a moderate scale; the Powell Survey, which focused on the southwest and the Grand Canyon region; and finally the Hayden survey, which surveyed the territory of Colorado as well as the last great unmapped region of the Lower Forty-Eight: the Yellowstone Basin.
The Colorado survey was sandwiched between Yellowstone surveys and conducted in the years 1873-75. Hayden expected Colorado to soon become an important region because of the arrival of the railroads, and thus decided to expend enormous resources in order to create what would be one of the most extensive regional surveys anywhere in the world.
Each year, Hayden would subdivide his team into four groups, each consisting of a number of geologists, cartographic experts, and scientists, with each group assigned to a specific area. Hayden would always reserve the most interesting of the regions for himself: that is how he came to personally map the area around Aspen. The details of this survey are immensely interesting. Please refer to Thomas P. Huber's work, linked to in our references, for more information on the survey.