Thursday, May 28, 2026

Geology of the National Parks in Pictures - Herbert Hoover National Historic Site

My next post about the Geology of the National Parks Through Pictures is from our move across the country from Utah to New York. Along the way we visited 13 National Parks as well as some other sites. This was the 13th, and final, National Park along the way.


You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

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Obligatory entrance sign photo


Herbert Hoover is notably the only geologist (to date) to have become president. His wife, Lou, was also a geologist, and the first woman to receive a geology degree from Stanford University. And while you would hope that a geologist would have many geological tidbits around his National Historic Site, there are not many across the park.

Schoolhouse

In front of the schoolhouse there is a sign that has a little geological tidbit about Hoover. It is assumed that Hoover attended school here from age 5 until ~10 or 11, after which he went to live in Oregon with his uncle after he was orphaned. Eventually, he attended Stanford and received a degree as a Geological Mining Engineer, with the photo in front of the school house here, showing Hoover as part of a geological survey squad in 1893.

Herbert Hoover Birthplace Cottage

Another site within the park, the Birthplace cottage, has some geology to it. The foundation of the birthplace cottage had been changed over the years, with the original foundation having been constructed using local boulders found on the prairie. The cottage was then purchased by another family and moved in 1889. However, it was then restored to its original location in 1934, when the Hoover family repurchased it. The stones used for the current foundation is a "local stone", however I can't find any more information on the specific rocks used. My guess is that it is a dolomite (a type of limestone), because the park sits upon several dolomite formations.

Geological map of Herbert Hoover National Historic Site and surrounding area. Image courtesy of the NPS.


The majority of the park sits upon the Silurian Age (~430 million years old) Scotch Grove Formation and the ~425 million year old (still Silurian) Gower Formation. Both of these are fossiliferous dolomites that formed in fairly shallow marine environments. These rocks are slightly younger than the bedrock below the nearby Effigy Mounds National Monument. If the stones for the birthplace cottage were quarried locally, it is likely that one of these two formations were the ones quarried. 


One of the most notable geologically related construction stones are the marble slabs used for the grave markers for both President Hoover and his wife, Lou. The marble slabs are noted as "Vermont white marble", however there is little information besides this to identify the quarry, region, or formation of the marble use. It is assumed that, due to the time period that these slabs would have been quarried, and the importance of the memorial (being a former president) that these are likely from the Danby Imperial quarry.


The Danby quarry is the largest underground marble quarry in the world. This quarry, located in the northeast flank of Dorset Mountain in Vermont, mines the Columbian member of the Lower Ordovician Shelburne Formation (~480 million years ago). These marbles were originally deposited as a limestone within a shallow marine environment. Then burial under other rocks and metamorphism from mountain building heated the limestones up and folded them, altering the minerology to produce the marbles as they are today. Blocks of marble from this quarry have been used in the New York Public Library, the Jefferson Memorial, Harvard Medical School, the U.S. Senate Building, Arlington National Amphitheater, the Supreme Court, and the United Nations building.


Although it is possible to find some of the bedrock along local stream channels, the majority of the bedrock within the park is located fairly deeply beneath glacial sediments (hence the original boulders used for the birthplace foundation) that were deposited during the early and middle Pleistocene Epoch (about 2.6 million years ago to 500,000 years ago). These glacial deposits are known as the Pre-Illinoian Alburnett and Wolf Creek formations, which comprise mostly of till, a glacial deposit that is essentially a clay rich mishmash of everything that can be thrown into one pile. Think of a glacier scouring the surface of the earth and then just dumping everything it picks up into a pile like a conveyor belt. That is till. 

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Thursday, May 14, 2026

Geology of the National Parks in Pictures - Effigy Mounds National Monument

My next post about the Geology of the National Parks Through Pictures is from our move across the country from Utah to New York. Along the way we visited 13 National Parks as well as some other sites. This was the 12th National Park along the way.


You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

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Obligatory entrance sign


Great Bear Mound

Created by ancestral people known as the Effigy Moundbuilders, the mounds served several different purposes. Primarily they were used for human burial purposes by piling soil, sod, and clay, along with other materials, in the shapes of animals over the bodies of the deceased. These shapes include birds, bears, water spirits, deer, turtles, beaver, buffalo, canines, and other animals, however the shapes are often difficult to identify along when viewed at ground level. The Lidar image below gives an excellent example of an aerial view of the mounds, with each of these marching bear mounds reaching around 20 meters in length. 

Lidar of the Marching Bear Group in the southern portion of the park. Image courtesy of the NPS via Wikimedia.

Found throughout the region, most of the mounds within the park are conical in design. However mounds, like the Great Bear Mound, form the shape of animals (pictured from ground level above). There are also linear and compound designs found within the park, but in far fewer numbers.

Types of mounds found at Effigy Mounds NM. Image courtesy of National Park Planner. 


The construction of at least some of the mounds began by first removing the sod or leafy humus from the forest floor. A square shaped pit was then dug out and human bodies were laid to rest within the pit. One of the excavated mounds held four bodies. Soil was then piled up upon the bodies along with rocks and clam shells. Cremation ashes mixed with baked reddish clay were mixed in with the final layer of earth on top of the mound. 


The location of the mounds, especially within this region, were generally along elevated surfaces. These mounds, in the picture above, are the end of a linear series of conical mounds that end at a promontory overlooking the Mississippi River (below). By placing the mounds at an elevated location they remained isolated from the flooding common to the shores of the Mississippi River.


All of the mounds within the park are located upon an elevated plain overlooking the Mississippi River, with tributary rivers, like the Yellow River adjacent to the entrance and Visitor's Center, carving deep valleys within the plateau. The plateau is comprised primarily dolostone (a more weathering resistant variety of limestone) and sandstone. Both provide a surface that is slow to erode away.

Prairie du Chien Group seen along the hike up to the mound plateau on the northern portion of the park. 

Geologically, the mounds sit upon the Lower Ordovician age (~480 million years ago) Oneota and Shakopee Formations, which make up the Prairie du Chien Group. These beds are primarily made up of dolomite, quartz sandstone, and sandy dolomite. There is also significant amounts of chert within the beds. Below the Prairie du Chien Group, you can also see the older, Upper Cambrian in age (~490 million years old), Jordan Sandstone along the parts of the park that border the Yellow River. Both of these formations were deposited when the area was inundated by a vast sea. The sea ebbed and flowed across the land, alternating periods of deep water deposits as well as shallow coastline deposits. When the water was shallower, sand would be deposited along the coastal waters. As the water deepened, limestones and dolostones (a variety of limestone that has a high concentration of magnesium within the crystal structure), were deposited from the bodies of sea life that slowly died over time.    


Glacially, Effigy Mounds is in the Driftless Area of Iowa, meaning that it was never covered with glaciers. While these elevated plateaus did not feel the effects of glacial activity, the neighboring Mississippi River was carved out by glacial meltwaters, with glacial debris filling up the river valley up to 150 feet. 

3 Mounds

While the park is primarily an archeological site, geology plays a major role. By providing the elevated location for the mounds, to suppling the materials used that were incorporated within the mounds, such as the dolostone, clay, along with the soil and sod, geology was a major contributor to the building of the Effigy Mounds. 

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