Merrill S. Stainbrook State Preserve

The 32.5-acre Merrill A. Stainbrook State Preserve features a unique combination of rich fossiliferous limestone and a rare display of glacial grooves. 

It is located seven miles north of Iowa City on the east side of Mehaffey Bridge, which crosses the Coralville Reservoir in northern Johnson County. 

About the Land

The property was acquired by the U.S. Army Corps of Engineers as part of the Coralville Reservoir project. The fossiliferous rock was revealed during construction of the bridge in the 1960s. 

The area was dedicated as a geological state preserve in 1969 in memory of Merrill A. Stainbrook (1897–1956), a scholar, teacher, and geologist who devoted much of his career to studying the fossils of the Cedar Valley limestones.

Directions

1. From the intersection of I-80 and Dubuque Street (exit 244) on the north side of Iowa City, take Dubuque Street north about 6 miles into the town of North Liberty. 
2. Turn north (right) onto Front Street (County Road F28), go north 0.75 mile, and curve east (right) onto Mehaffey Bridge Road. 
3. Follow Mehaffey Bridge Road about 2.5 miles to the preserve just past the Mehaffey Bridge over Coralville Reservoir. 
4. Park on the shoulder and walk over a footbridge on the southeast (right) side. A path leads to an interpretive sign and the rock surface containing the glacial grooves.

Geology

The limestone exposed here belongs to the Devonian-age (375 million years old) Cedar Valley Group. It includes about ten feet of the Rapid Member and nearly twelve feet of the overlying Coralville Formation. 

Brachiopods & Corals

The Rapid Member contains large, well-preserved brachiopods (shellfish), and the Coralville Member contains well-preserved colonial corals, some several feet in diameter. 

Limestone

About three feet of State Quarry Limestone is also present above the Cedar Valley Group. Forty feet of the State Quarry Limestone may also be seen at the nearby Old State Quarry State Preserve. 

Over 500,000 years ago, the surface of the State Quarry Limestone here was beveled and grooved by Pre-Illinoian glaciers. The grooves were formed parallel to the direction of the ice movement from northwest to southeast. 

Visitor Information

Numerous school groups from the area and the University of Iowa geology classes visit the site several times a year. 

Other geological areas in the vicinity include Old State Quarry and Palisades-Dows State Preserves, Palisades-Kepler State Park, and the Devonian Fossil Gorge.