The Niagara Escarpment is a limestone bluff formation that arches for a thousand miles around the Great Lakes, including along Green Bay, and is part of the same formation over which Niagara Falls plunges in New York. Its lower layers of soft, erodible shale are protected by a hard cap of dolomite limestone; as the uplifted shale edges erode, the hard limestone snaps off to form steep cliffs. Along these bluffs, cedars as old as 1,200 years cling to the escarpment and rare plants grow in the crumbled rocks below. The escarpment rises in cliffs 250 feet above Green Bay, providing lingering sunset views over the water, while the dolomite bedrock slopes eastward and disappears beneath Lake Michigan. The Door Peninsula lies on the western rim of the geologic Michigan Basin, whose rim forms Door County's bayside cliffs while the bowl's incline slopes east below Lake Michigan. Jens Jensen, the renowned landscape architect and conservationist, was inspired by the grand view atop this hill and in 1935 chose a site overlooking Green Bay for his folk school, The Clearing, set in forest openings high above the bay as a place where busy people could clear their minds and reconnect with nature.