The Great Lakes Region was once covered by glaciers more than one mile thick, and as these heavy ice sheets advanced and retreated they sculpted the land below. About 10,000 years ago, after global temperatures rose, the last glacier retreated northward from Michigan, leaving behind the landforms and waterways seen there today. In this area, glacial sediment is 250 to 800 feet thick, so exposed bedrock is absent, but glaciers also carried boulders from as far away as northern Canada, creating glacial erratics. Receding ice sometimes left buried ice blocks that melted and formed kettles, and some filled with water to become kettle lakes; most Michigan inland lakes, including nearby Higgins Lake, were created this way. Grayling stands on an outwash plain of sand and gravel deposited by meltwater, with the five upland plateaus called the Grayling Fingers just to the north and an east-west moraine to the south. During the white pine logging era from 1870 to 1900, most of Michigan's forests were clearcut for timber, but the largest surviving stand of old growth trees is in Hartwick Pines State Park. In 1927, Karen Hartwick, daughter of lumber magnate Nels Michelson, bought more than 8,000 acres from the Salling & Hanson Logging Company and donated the land to the State of Michigan to memorialize her husband Edward, who died in Europe while serving in World War I. The deed required a memorial building dedicated to Edward Hartwick and a logging history museum, and the gift provided jobs during the Great Depression, a refuge for native plants and wildlife, and a place to experience towering white pines cut down elsewhere. Of the donated parcel, 85 acres were old growth trees, and 49 acres remain visible today. At the park's dedication on July 19, 1935, Governor Frank D. Fitzgerald praised Karen B. Hartwick for preserving a beauty that might otherwise have been lost, and surveyor John J. Higgins, recalling his 1869 work in Crawford County, remembered the magnificent tall, straight pines and said reforestation would take a very long time.