The lower Mississippi River spilling into the Gulf of Mexico may be 208 million years old. It likely began as a perpendicular fault line associated with the continental separation that formed North and South America. On the other hand, the upper Mississippi River in its current position is only 11 thousand years old. It formed from glacial water flows over thousands of years carving its channel, valley, and broad watershed. After scouring from clean glacial waters, tributaries then brought sediment-filled waters to the Mississippi. This process began reducing the river’s depth and continues today.
The UMRV boundary contains formidable amounts of loess sediments loosened from retreating glaciers to the west and whipped into the air by warming temperatures for deposition along the upper Mississippi River Valley. These fine loess elevations were then cut into deep, expansive hill and valley configurations by torrid overflows of glacial lakes outside the region to the north.
Elevations in the UMRV boundary range from 660 feet on valley floors to 1310 feet on the highest ridges. Sloping to hilly uplands are dissected by both large and small tributaries to the upper Mississippi River. Bottom land along all streams is narrow, and some ridge tops are broad with undulating slopes. Local relief is mainly 10 to 20 feet, but as much as 50 to 100 feet on valley walls along the major streams. Relief is as much as 250 feet on the Mississippi River bluffs above the river.
The UMRV boundary includes average annual precipitation from 30 to 38 inches. Two-thirds or more of the precipitation falls during the freeze-free period. Most of the rainfall occurs as high-intensity, convective thunderstorms during the summer. Snowfall is common in winter. The average annual temperature is 42 to 50 degrees F. The freeze-free period averages about 175 days ranging from 145 to 205 days.
In most years the moderate precipitation in the UMRV boundary is adequate for crops and forage, but in years of little or no precipitation yields are reduced on soils that are shallow over bedrock. The many springs, streams, and farm ponds are additional sources of surface water in the area. The surface water is abundant and generally of good quality. Poor water quality in stream reaches primarily is the result of non-point sources of sediment, nutrients, and pesticides from agricultural land or wastewater discharges downstream from larger cities. Ground water is abundant in glacial outwash deposits in most of the region’s river valleys.
Water here is moderately hard or hard but generally of very good quality. The level of total dissolved solids is typically less than 250 parts per million. The supply of ground water varies in the uplands where the sandstone and dolomite layers in the Jordan and Prairie du Chien aquifers usually provide adequate yields to wells. Water from these aquifers is suitable for all uses, although the level of total dissolved solids approaches 1,000 parts per million in some areas.
The Mississippi River flows through the area dividing Minnesota and Wisconsin and then Iowa and Illinois. The petition’s Mississippi River tributaries are represented by the Kickapoo, Wisconsin and Pecatonica Rivers in Wisconsin; the Zumbro, Whitewater and Root Rivers in Minnesota; the Upper Iowa, Turkey, Yellow, Volga, Maquoketa and Wapsipinicon Rivers in Iowa; and the Apple, Plum, and Rock Rivers in Illinois.