Chapter 3: Geologic Structure and Landforms
Geologic interpretation of images begins with the identification of lineaments, “regional linear features caused by linear arrangement of regional morphological features such as streams, escarpments, and mountain ranges and tonal features that in many areas are the surface expressions of fractures or fault zones.”[i] The emphasis in this section is on geologic structures and landforms, both of which can be easily identified on air photographs and other images.
The sequence followed here is that often found in geomorphology books. Geologic structures and structurally controlled landforms are illustrated first, followed by images of mass wasting and of the results of the agents of erosion—running water, ground water, ice, wind and the sea. The meandering rivers of southern
3.47: Ground Moraine Topography East of Rapid City
The photograph shows part of the Minnedosa-Reston Till Plain.[i] It includes all or part of sections 3, 4, 5, 8, 9, and 10 of township 13, range 18WI and a very small part of sections 32, 33, and 34 of township 12, range 18WI near the hamlet of Moore Park.
A layer of till, the parent materials for which are Cretaceous shale of local origin, Paleozoic limestone and dolomite from the northeast, and Precambrian rocks from the Canadian Shield to the north, covers much of the surface of southwest
The soils developed on the till are generally black chernozems,[iii] but they vary greatly over short distances depending on the topography and drainage. On the higher ground, at the tops of knolls, much of the fine-grained organic material has been removed by a combination of rain splash and wind erosion. The resulting coarse-grained, light-coloured soils appear light-toned on the photograph 3.
The combination of hummocky terrain and rapid soil variation make large-scale farming difficult. In the east 4 and south 5 much of the land is still wooded, but in other areas arable agriculture is practised. Light-toned fields have been planted to cereal crops 6 (probably wheat given the year of the photograph). In some cases harvesting is underway and stooks have been left in fields 7,[iv] and in another case a field has been partly cut 8. Many fields have been left fallow 9, and in these the light-toned hillcrests are especially marked. This area experiences a dry climate, and, as a result, dugouts have been constructed 10 to provide water, principally for farm animals.
Population density is low; only 3 farms 11 can be identified in the area of just over 4 square miles (10.8 square kilometers). The land is divided into sections with gravel roads along some section lines 12 although in one case there is an anomalous jog to the west 13 to avoid a wooded area. The CP railway line in the south 14 was abandoned long ago.
Figure 3.47: Ground Moraine Topography East of Rapid City
Vertical air photograph: A11677-23
Flight height: 9420 feet a.s.l.; lens focal length: 153.75 mm
Date: September 3, 1948
Scale: 1:15,500 (approx.)
Location: Townships 12 and 13; Range 18 WI
Map sheets: 1:250,000 62J Neepawa
1:125,000 62J/SW Neepawa
[i] See Welsted, Everitt and Stadel, op. cit., 1996, figure 2.9, 21.
[ii] Mollard and Janes, op. cit. 1984, 49, writing about ground moraine near Medora.
[iii] See Welsted, Everitt, and Stadel, op. cit. 1996 figure 4.3, 46.
[iv] This is an old method of harvesting no longer used.