of Harrisburg. The Saline flowed towards the Ohio and flooded every spring in events called Freshets. The locals called the island "Crusoe's Island". When the area was drained, homes and businesses were built in the floodplain, and it became prone to serious flooding for years to come. The town square in the center of town is a sandstone bluff above sea level, one of the first that start the Shawnee Hills to the south. Topographic maps show the bluffs that rise from the Saline River that wraps the northeast part of the city. Harrisburg is located at the ending point of the Laurentide Ice Sheet, which covered about 85 percent of Illinois. The edge of Illinoian ice sheet(s) lay further south than the southernmost extent, i.e. Douglas County, Kansas, of any of the Pre-Illinoian ice sheets. Cottage Grove Fault System After the 5.5 Richter Scale magnitude 1968 Illinois earthquake, scientists realized that there was a previously unknown fault under Saline County, just north of Eldorado near Harrisburg. This fault is called the Cottage Grove Fault, a small tear in the Earth's rock running west–east, in the Southern Illinois Basin. The fault is connected to the north–south trending Wabash Valley Fault System at its eastern end. Seismographic mapping completed by geologists reveal that monoclines, anticlines, and synclines are present within the region; these signs suggest deformation during the Paleozoic era coincident to strike-slip faulting nearby. A focal mechanism solution of the earthquake confirmed two nodal planes both striking north–south and dipping approximately 45 degrees to the east and to the west. This faulting suggests dip-slip reverse motion, and to a horizontal east–west axis of confining stress. The rupture also occurred partially on the New Madrid Fault, responsible for the great New Madrid earthquakes in 1812, consisting of the most powerful earthquakes to hit the contiguous United States. Cityscape During the early 20th century, urbanization of the city due to the geographical feature of "Cruesoe's Island" and surrounding coal mining property created a density not seen in many cities of its size. The city at the time with a population nearing 10,000 was forced to tightly cram homes and businesses upon the sandstone outcropping less than a square mile in diameter leading many to build their buildings with multiple stories around the town square. The Saline County courthouse and square have gone through many transformations within the past 100 years. In the