Minnehaha Creek extends from Lake Minnetonka in the west and flows east for 22 miles (35 km) through several suburbs west of Minneapolis, and continuing through south Minneapolis. The watershed for the creek covers 181 square miles (470 km2). Along the creek is a 53-foot (16-meter) waterfall, Minnehaha Falls, which is situated 3/4 of a mile from where the stream empties into the Mississippi River.
Minnehaha Falls is geologically linked to Saint Anthony Falls, which is the only waterfall on the Mississippi River. Roughly 10,000 years ago, St. Anthony Falls several miles downstream on the Mississippi River at the confluence of the glacial River Warren (at present-day Ft. Snelling). Geologically, the area has a sandstone layer beneath a layer of limestone. Over the centuries, water in the river beds broke through the limestone layer, and the churning at the bottom of the falls ate away at the soft underlying sandstone. Eventually, the hard limestone cap was unsupported and broke off. Thus St. Anthony Falls receded, moving upstream at a rate of about 4 feet (1.2 m) per year. As St. Anthony Falls on the Mississippi River moved past Minnehaha Creek, a second falls was created, Minnehaha Falls, which also continued to move upstream to its present site in the park.
An island in the Mississippi River near Minnehaha Creek once existed; the receding St. Anthony Falls divided into two as it passed around the island. The falls in the channel farthest from Minnehaha Creek reached the upstream end of the island first, cutting off water to the west channel and resulting in an “abandoned waterfall” at the north end of the channel. The abandoned west channel is now a grassy cul-de-sac known as the “Deer Pen”. Locating the abandoned waterfall was made difficult in recent years since the Deer Pen was partially filled with tons of fill dirt from nearby construction projects. Today, the mouth of Minnehaha Creek where it joins the Mississippi River is the lowest surface point in the city of Minneapolis at 686 ft (209 m) above sea level.
Erosion within the last century has resulted in a falls that is fairly narrowly channeled and vigorous, notably after a heavy rain. Photographs of the waterfall from the 19th century show a much wider, curtain like character to the falls. When the creek is dry, the older, much-broader ledge can be observed. If there were sufficient interest and funding, some remedial work could theoretically restore the 19th-century appearance of the falls. Due to extremely cold winter temperatures, the falls freeze, creating a dramatic cascade of ice that can last well into the spring. If there is a rain shortage in the autumn, the falls may virtually dry up. In the summer, especially in the rainy months of June and July, the flow can be surprisingly forceful.
…
