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The Thatcher Woods River corridor represents a cross- section of the Des Plaines river valley in which the river flows over the sediment of the ancient lake plain of glacial Lake Chicago. Within these Forest Preserves are excellent remnants of high quality flood plain forest. Many of the floodplain forest trees exceed one meter in diameter and may be among the largest examples in the Chicago region. The area is unique in that the natural communities of floodplain forest integrate with mesic (moisture balance) upland forest and mesic oak savanna in a contiguous landscape - showing the transitions of plant associations from the river floodplain to upland forest and savanna. This is especially evident in the GAR and Thomas Jefferson units. Elevations reach 625 feet in the upland regions, dropping, sometimes abruptly, into the river floodplain reaching 610 feet along the river bank. Transitory ponds occur in glacial scars of the bottomland areas, while moisture conditions in the upland regions are balanced. Often times, where the foot paths cross natural scars or ravines in the landscape, muddy or flooding conditions exist. |