This large gap, called the Lower Narrows, is one of three major gorges that cut through the 50 mile circumference of the Baraboo Range. These gorges were created by rivers more than 500 million years ago and then buried by sediments in a vast sea over the next 150 million years. Wind, water and glacial erosion have once again exposed the gorges. The Baraboo River now flows through the Upper Narrows gorge near Rock Springs, entering a basin surrounded by the Baraboo Range, and exits here at the Lower Narrows. Notable for its ancient rock formations, the Lower Narrows features vertically-tilted Precambrian pink Baraboo quartzite rock ribs on both walls of the gorge. Red rhyolite rock, over 1.5 billion years old, is visible on the northeast flank of the Lower Narrows along Highway 33. Devil's Lake, in the longest and deepest gorge of the Baraboo Range, was formed when the gap was blocked by glacial debris 15,000 years ago. Of the Baraboo Range, geologist and president of the University of Wisconsin, Charles R. Van Hise commented: "I know of no other region in Wisconsin which illustrates so many principles of the science of geology."