Gator Girl Rocks

Rockhounding Iowa

Iowa is a good state for rockhounding.  The state primarily is known for its ‘Keokuk geodes.’  Iowa, of course, was under a Cretaceous shallow sea and, as a result, has sedimentary deposits.  Accordingly, Iowa also has fossils as well as several caves.  In addition, numerous meteorites have been recovered in Iowa (for meteorite hunters, a meteorite fall on the Iowa terrain is much, much more desirable than trying to find meteorites in the Rocky Mountains or heavily forested areas).

State Rocks, Gemstones, Minerals, Fossils, & Dinosaurs

Rockhounding Tip:  Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders.  Ordinarily, states with significant mineral deposits, valuable gemstones, fossils, or unusual or significant rock occurrences will designate an official state mineral, rock/stone, gemstone, fossil, or dinosaur to promote interest in the state’s natural resources, history, tourism, etc.  Accordingly, such state symbols often are a valuable clue as to potential worthwhile rockhounding opportunities.

State Rock:  Iowa Geode (1967)

Iowa designated the Iowa geode as its official state rock in 1967.  The state is well known for its geodes.  The word "geode" is derived from Latin and means "earthlike," a reference to their rounded shape.  Most Iowa geodes are roughly spherical, often lumpy or cauliflower-like in external form, with diameters typically ranging between about two and six inches (specimens up to thirty inches are known).  Geodes are found in limestone formations and have a hard outer shell.  The most prized geodes have hollow interiors, although many geodes are solid objects in which crystal growth has filled most or all of the interior volume.  Geodes from the Keokuk area contain a variety of minerals, but quartz and calcite are dominant in most.  Southeastern Iowa is one of the state's best geode collecting areas.

 

Rockhounding Resources

Iowa Geological & Water Survey

Mid-America Paleontology Society

 

• Robert Wolf, Fossils of Iowa: Field Guide to Paleozoic Deposits (2006).  
• Wayne I. Anderson, Iowa’s Geological Past: Three Billion Years of Change (1998). 
• Stephen Sinotte, The Fabulous Keokuk Geodes – Volume I – Origin, Formation, & Development in the Mississippian Lower Warsaw Beds of Southeast Iowa and Adjacent States (1969).
• June Culp Zeitner, Midwest Gem, Fossil, & Mineral Trails: Prairie States (Rev. ed., May 1998 – first published in 1955). 
• June Culp Zeitner, Midwest Gem Trails: Field Guide for the Gem Hunter, the Mineral Collector, and the Tourist (3d. Rev. ed., 1964 – originally published in 1956). 
• Allan W. Eckert, Earth Treasures Vol. 3 - Northwestern Quadrant (1986; reprint in 2000).
• James Martin Monaco & Jeannette Hathway Monaco, Fee Mining & Mineral Adventures in the Eastern U.S. (2d ed. 2010).
• Kathy J. Rygle & Stephen F. Pedersen, Northwest  Treasure Hunter's Gem & Mineral Guide (4th ed. 2008).

Museums of Interest to Rockhounders

University of Iowa Museum of Natural History
University of Iowa – Iowa City, Iowa
The museum’s ‘Iowa Hall’ features a ‘Geology of Iowa’ exhibit that covers five hundred million years of geologic history.  The University of Iowa also has an extensive paleontological collection.

 

University of Northern Iowa Museum
Cedar Falls, Iowa
The museum includes a permanent exhibit pertaining to rocks, minerals, & fossils.

 

Madison County Historical Society
Winterset, Iowa
The museum includes exhibits on minerals and rocks.

 

Sanford Museum & Planetarium
Cherokee, Iowa
The museum exhibits local rocks and fossils.

 

 

Places to Visit - Interesting Sites To See

Old Capitol Building
Iowa City, Iowa
The largest fragment of the Marion Meteorite is on display in the Old Capitol Building.  The Marion Meteorite fell south of Marion in Linn County just before 3:00 p.m. on February 25, 1847, the day that legislation establishing the University of Iowa was signed into law in Iowa City, which was then the State Capitol.  Residents of Iowa City were alarmed by the series of loud explosions to the north.

 

Geode State Park
Henry, Iowa
Geode State Park, in southeastern Iowa, is named for the occurrence of geodes.  The park office has a display of geodes.  Note:  In Iowa, it is illegal to remove geodes from state parks.

 

Manson Crater – aka the Manson Impact Structure
North central Iowa near Manson, Iowa
The Manson Crater is the location where a mountain-sized meteorite hit the planet – at 45,000 miles per hour – about 74 million years ago.  The crater is not visible from the surface.  Rather, it is deep underground buried by glacial till from the glaciers of the last ice age.

Devonian Fossil Gorge
Coralville, Iowa
Following a flood in 1993 (and again in 2008) that caused Coralville Lake to overflow, a 375 million year old limestone seabed was revealed.  The Devonian Fossil Gorge is located along the Iowa River.  Visitors can see various marine fossils including brachiopods, corals, trilobites, and crinoids.  The U.S. Army Corps of Engineers has a Visitors’ Center at the Dam that has geologic information and fossil displays.

 

Grotto of the Redemption
West Bend, Iowa
Located in north central Iowa, the Grotto of the Redemption is a religious monument.  The structure consists of nine grottos depicting scenes in the life of Jesus.  The structures contain a very large collection of rocks, minerals, gemstones, and fossils from around the world.

 

Rockhounding Sites for Children & Families

Geodes
Keokuk, Iowa
Although geodes are known from many localities around the world, one of the most productive and famous collecting regions is encompassed within a 50-mile radius of Keokuk, Iowa.  Iowa's renowned ‘Keokuk geodes’ can be found in specific stream drainages and excavations in parts of southeastern Iowa (especially in Lee, Henry, and Van Buren Counties), including the area near Geode State Park.  Most geodes are derived from strata of the lower Warsaw Formation, a widespread rock unit of Mississippian age.  Muds deposited in a shallow sea about 340 million years ago were primarily calcium carbonate and clay, and were subsequently lithified to form the shales, shaley dolomites, and limestones that we see today.  Fresh geodes can be dug out of exposures of the lower Warsaw Formation, where they are concentrated in certain layers.  Where water and streamflow have eroded these strata, concentrations of geodes may accumulate in stream channels.  Although the bulk of Iowa's geodes are derived from the Warsaw Formation, geodes also are known from other formations of Devonian and Mississippian age at scattered localities in eastern and central Iowa.

 

Devonian Marine Fossils
Floyd County Fossil & Prairie Park Center – Rockford, Iowa
This public park, located west of Rockford, is one of the few geological preserves that allows specimen collecting for private use.  The site, which was a former clay pit for a brick and tile company, is a Devonian strata with abundant marine fossils, including brachiopods.  The soft sediment allows fossils to weather out.