In westernmost Iowa, the Loess Hills rise as much as 200 feet above the Missouri River flood plain in a narrow north-south band 200 miles long, with steep western bluffs and more gently rolling eastern slopes. Their unusually deep wind-deposited loess, in some places as much as 200 feet thick, makes them a rare geologic feature matched in extent only by Shaanxi, China. During the Ice Age, glaciers ground rock into fine sediment, meltwater spread it across the Missouri River valley, and strong winds carried silt eastward, where repeated deposition over thousands of years built the hills layer by layer. The Loess Hills include the Loveland Loess, Pisgah Loess, and Peoria Loess, and exposures also reveal glacial sand and gravel, older limestone, volcanic ash from eruptions near Yellowstone more than 710,000 years ago, and glacial erratics such as Sioux Quartzite boulders carried far from their source. Monona County's Freedom Rock is one such erratic, a 432 cubic foot granite boulder weighing about 75,600 pounds, left behind when ice melted about 12,500 years ago. It was uncovered in 1979 at the bottom of the Dunlap Pits near Dunlap, Iowa, sat for more than 30 years at Peter's Aggregate Company in Onawa, was donated after the property was sold to Northern Ag, moved to its present site on August 30, 2013, and painted by artist Ray "Bubba" Sorensen II on August 17-25, 2016, for a project coordinated by William A. Wonder. Its illustrations honor veterans, including Cpl. Llythaniele Fender, who was killed in 2007, and 2nd Lt. Archie Steen, a World War II veteran.