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City of Mounds View Page 6 Local Surface Water Management Plan 435-08-135 Figure 2.2 – Soils Classification Map 2.4 GEOLOGY The geology of the region surrounding Mounds View is the result of two different geologic processes: Warm, shallow seas covered the area and created conditions for the formation of sedimentary rocks. These formations are present as bedrock in the area. Glacial processes have resulted in the development of surficial geology, and therefore, current landforms. The City’s geology is generally ranges from 150 to 300 feet of glacial till and outwash overlying sedimentary bedrock. The bedrock units beneath the City are marine sedimentary rocks primarily of the Upper Cambrian to Middle Ordovician ages (450 to 500± million years old). Ranging from deeper/older bedrock to relatively shallow/young bedrock, the specific geologic units include the St. Lawrence/Franconia formation, Jordan Sandstone, and the Prairie du Chien group. Glacial influence on this area began around 2.5 million years ago and continued until about 10,000 years ago. However, the last episode of glaciation created the present landscape features in this area and across Minnesota. This episode lasted from about 35,000 to about 10,000 years ago. Two major glacial ice sheet movements constituted this episode during what is known as the late Wisconsin glaciation. The first, the Superior lobe, advanced from the north. The second, the Grantsburg sublobe, advanced from the southwest. In one period of retreat during the Superior lobe glaciation, melt waters deposited a thick layer of glacial outwash made up of sand and gravel over a widespread area including Mounds View.