アイオワの天然記念物・トップ20

Siewers Spring, located a mile south of Decorah, is Iowa’s second-largest natural spring. It’s the vital water source for the Chuck Gipp Decorah Fish Hatchery, where rainbow trout are raised and visible to the public. Enjoy walking paths, picnic spots, and streamside fishing at the spring and nearby Trout Run. With a history dating to 1832, Siewers Spring once powered local industries before becoming a state park and hatchery in the 1930s, with Civilian Conservation Corps-crafted limestone buildings.

Siewers Spring, located a mile south of Decorah, is Iowa’s second-largest natural spring. It’s the vital water source for the Chuck Gipp Decorah Fish Hatchery, where rainbow trout are raised and visible to the public. Enjoy walking paths, picnic spots, and streamside fishing at the spring and nearby Trout Run. With a history dating to 1832, Siewers Spring once powered local industries before becoming a state park and hatchery in the 1930s, with Civilian Conservation Corps-crafted limestone buildings.

Pulpit Rock, a prominent limestone bluff in Decorah, Iowa, is a picturesque natural landmark in Will Baker Park. This striking geological formation, sculpted by centuries of erosion, offers dramatic views of the Upper Iowa River and the surrounding cityscape. A moderately challenging one-mile loop trail, featuring some steep sections and stone steps, leads hikers to the summit. From this vantage point, visitors are rewarded with panoramic vistas of the Decorah Community Prairie and the scenic rolling hills characteristic of Iowa's Driftless Area.

The water that feeds Dunning Spring comes from near the base of the Galena Aquifer. Beneath this aquifer is the much less permeable Decorah Shale, which acts as a "confining bed" or "floor" for the aquifer. When the Decorah Shale is exposed near the surface of the land, particularly on the sides of river valleys, it causes groundwater to discharge. This process creates beautiful waterfalls and springs, such as Dunning Spring.

About 465 to 470 million years ago, a meteorite struck near present-day Decorah, Iowa, creating a 3.5-mile (5.6 km) wide impact crater buried beneath the city's surface. Although this highlight is named “Decorah Impact Crater Marker”, at the time of my most recent hike to this highlight, on August 2, 2025, there was no marker or monument nearby. However, there is a large bronze medallion set in concrete marking the precise meteorite impact site located about 0.2 miles west-southwest of this highlight.. The marker can be found at GPS coordinates 43.31580, -91.77474. I have made this location a komoot highlight as well. The bottom of the impact crater now lies about 300 feet below the marker due to geological changes that have occurred over the millennia following the meteorite strike. The crater and its discovery are significant because it is one of fewer than 200 recognized impact structures on Earth. It has preserved a unique fossil record of ancient life, including the nearly 6-foot sea scorpion known as Pentecopterus decorahensis.

The visitor center is a great place to begin your exploration of Effigy Mounds National Park. There is an exhibit that describes the natural and human history of the area. There is a small bookstore. And if you are into collecting National Parks cancellation stamps, you can also get those. In addition, this is the starting point for all the trails in the North, South, and more recently acquired Heritage areas of the park.

I found this fascinating bit of history about Nazekaw Point on the Effigy Mounds National Monument Facebook page: "The town of Nazekaw: Did it exist? In 1856, two speculators from Prairie du Chien, Bernard W. Brisbois and Herculus Dousman, purchased property at the mouth of the Yellow river from the federal government. The speculators created the paper town of Nazekaw (also known as Nazeka and Nazekaw) on the south bank of the Yellow River, and sold the surrounding lots to farmers. Multiple sources indicated the town included a post office, stockyard and gristmill between 1858 and 1862; however, other sources claim this is a “mythical” town that was only laid out on paper. We may never know if it did exist, but if visitors hike our South Unit trail, they can visit Nazekaw Point, which is a beautiful overlook of the mouth of the Yellow River and think about what might have been."

The hike to Nazekaw Point from the Effigy Mounds National Monument visitor center is 2 miles roundtrip, 350 feet elevation gain, 1 hour. This hike features a view of the Mississippi River. Hikers will pass one conical mound, one bear-shaped mound, and two linear mounds.