Geological maps are often amongst the most colourful of all the cartographic genres, with the majority using a wide range of colours to show the land beneath our feet. One of the first recognized geological maps produced in this way was William Smith’s celebrated map of England and Wales, from 1815, featured in an earlier entry in this blog, http://blogs.bodleian.ox.ac.uk/maps/2015/01/ . Towards the end of the Nineteenth Century the Ordnance Survey  started to produce detailed, and often beautiful,  geological maps of Britain and Ireland, something which continues to this day with the British Geological Survey (https://www.bgs.ac.uk/).

This map of the Black Hills of South Dakota is a variation on the usual method of geological representation. The publishers, the United States Geographical and Geological Survey of the Rocky Mountain, Region, have used four different symbols of birds in flight to show the underlying

Bird’s eye view of the Black Hills…1879. F6:49 (12)

geology of the region.  A lack of any compass directions, text or scale on the map leaves a confused view of a complicated geological area. The Black Hills region has been dated back as far as 1.8 billion years, and was formed by magma deposits released during the movement of tectonic plates during the event known as the Trans-Hudson Orogeny (orogeny is a term used to describe geological events that cause major changes in the appearance of the Earth due to tectonic movement). The dramatic rings around the main area are caused by anticlines surrounding a dome (an anticline is a geological fold where strata are pushed together).

The Black Hills has a history as complex as its geology. Long been a site of spiritual importance the Hills took on a political significance after treaties giving the lands in perpetuity to the Lakota Indians in 1868 were ignored with the discovery of gold in 1874, and with defeat in the Great Sioux wars in 1876 the tribes were forcibly moved to reservations outside of the Black Hills area. A ruling in the U.S. Supreme Court in 1980 stated that the relocation of the tribe was illegal, and that the Lakota were entitled to compensation, something which the Lakota refuse to accept as they believe that the only acceptable outcome is the return of the Black Hills. Mount Rushmore is on the eastern edge of the Black Hills and just across the border into Wyoming is the Devil’s Tower National Monument, created in 1906 and the first National Monument in the United States.

At the top of the map, just off the scan shown here, is the text ‘Dept. of the Interior, U.S.G and G. Survey, J.W. Powell in charge’. The U.S. G. and G. is the United States Geographical and Geological Survey, now called the U.S. Geological Survey and still producing maps to this day. J.W. Powell was an important figure in both the surveying and the exploration of the American West. John Wesley Powell was the second director of the U.S. Geological Survey but is remembered more for leading expeditions down the Colorado and Green Rivers, culminating in the first navigation through the Grand Canyon. A journey even more impressive considering that Powell had lost an arm during the Battle of Shiloh in 1862.

The area of the Black Hills, hard up against the border with Wyoming, shown on a more conventional geological map. The main part of the hill is schists (speckled brown) and granite (brown) surrounded by a ring of sandstone (light blue) and limestone (darker blue).This band of sandstone and limestone corresponds with the flat plateau of the western part of the raised dome in the earlier map.

Geological map of South Dakota, 1951. F6:49 (6).