Geology of Minnesota

Bedrock geologic map illustrating the main geologic regions of Minnesota. Igneous bodies lie across the northern half of the state, with intrusions throughout the northwest and basalts and other igneous rocks of the Duluth Complex and Beaver Bay Complex from the Midcontinent Rift System bordering Lake Superior in the northeast. In the southeast along the Mississippi River, up through the Twin Cities, canyons carve into Cambrian and Ordovician bedrock that were formed in shallow tropical seas that covered southern and south-central Minnesota during that time. The geology of the southwest includes old rocks, the 3.6 billion year old Morton Gneiss and the Paleoproterozoic Sioux Quartzite, overlain by the Cretaceous sedimentary sequence that includes the Dakota Sandstone, Niobrara Formation, and Pierre Shale, and is continuous across much of the western Midwest to the eastern slopes of the Rocky Mountains. Central Minnesota contains an ancient fault system from the Penokean orogeny.

The geology of Minnesota comprises the rock, minerals, and soils of the U.S. state of Minnesota, including their formation, development, distribution, and condition.

The state's geologic history can be divided into three periods. The first period was a lengthy period of geologic instability from the origin of the planet until roughly 1,100 million years ago. During this time, the state's Precambrian bedrock was formed by volcanism and the deposition of sedimentary rock and then modified by processes such as faulting, folding and erosion. In the second period, many layers of sedimentary rock were formed by deposition and lithification of successive layers of sediment from runoff and repeated incursions of the sea. In the third and most recent period starting about 1.8 million years ago, glaciation eroded previous rock formations and deposited deep layers of glacial till over most of the state, and created the beds and valleys of modern lakes and rivers.

Minnesota's geologic resources have been the historical foundation of the state's economy. Precambrian bedrock has been mined for metallic minerals, including iron ore, on which the economy of Northeast Minnesota was built. Archaen granites and gneisses, and later limestones and sandstones, are quarried for structural stone and monuments. Glacial deposits are mined for aggregates, glacial till and lacustrine deposits formed the parent soil for the state's farmlands, and glacial lakes are the backbone of Minnesota's tourist industry. These economic assets have in turn dictated the state's history and settlement patterns, and the trade and supply routes along the waterways, valleys and plains have become the state's transportation corridors.