In unglaciated parts of the state and beneath Quaternary deposits in the north is the Pliocene Mounds Gravel, unconformably atop older rocks and sediments. The Mounds Gravel remains as gravel alluvium from the Teays River, which once flowed north of current day St. Louis transporting sediments shed by the rising Rocky Mountains. Some geologists have suggested that the Mounds Gravel originated from erosion of the Central Highlands, when a large river flowed south through Kansas and Oklahoma to the Gulf of Mexico, until it was rechanneled to the present Mississippi River during the Illinoian glaciation. As Missouri experienced terrestrial erosion in the Pliocene, the Ozark Dome uplifted. Missouri did experience the Pleistocene glaciations, with the most recent glacial till from 600,000 years ago. A small lobe of ice pushed across the Mississippi River in the vicinity of St. Louis 200,000 years ago. The route of the Ancestral Kansas River rapidly eroded and filled with sediment in the area of Kansas City during periods of glacial melting and outwash. Till in northern Missouri is up to several hundred feet thick, sometimes containing cobbles and boulders, with an overall tan to red-brown color. 38th Parallel Lineament The Thirty-Eight Parallel Lineament is one of Missouri's unique structural features, a 10- to 20-mile wide area of folds, faults and shattered bedrock from the Kansas state line to Vernon County to the Mississippi River in Ste. Genevieve County. It contains the widespread Ste. Genevieve Fault and pockets of Paleozoic rock—particularly eight locations with broken, but rearranged groupings of igneous and sedimentary rocks together. Hypotheses suggest possible origins ranging from cryovolcanoes to pent up gas tearing through Paleozoic rocks and bringing up more ancient igneous rocks. Natural resource geology Galena is the official state mineral of Missouri and lead mining began in the 1720s in Madison County, spearheaded by French miners. The state is the leading extractor of lead in the U.S., both from galena and sphalerite. The minerals are sourced from Mississippi Valley Type deposits, deposited through hydrothermal activity. The Old Lead Belt and Tri-State Area were mined significantly before World War II, with new deposits found since in the southeast. The new deposit is known as the Viburnum Trend and spans Iron County and Reynolds County, with secondary production of copper, cadmium and silver, housed in the Bonneterre Dolomite between 600 and 1500 feet deep. During the late Cambrian, stromatalite beds shielded carbonates forming