Ryan Clark’s office is filled with rocks.

There are rocks on top of filing cabinets, rocks on metal carts, and rocks in boxes.

There are rocks big enough for a child to perch upon, and others the size of marbles.

There are several examples of Iowa’s state rock, the geode, as well as fossilized sea snails, fragile remnants of a prehistoric sea that once surged with life. 

“I know, I know. I’ve got a lot of rocks in my office,” says Clark, a geologist for the Iowa Geological Survey (IGS), a division of University of Iowa IIHR—Hydroscience and Engineering and the state’s go-to source for information about water, minerals, rock, soil, and energy resources. “It can get a little bit Indiana Jones here sometimes.”

To say that Clark knows a little about rocks would be a Jurassic-sized understatement. And the rocks he keeps in his office are just a sampling of what’s stored in the adjoining warehouse, a place he calls the “rock library.”

The IGS warehouse, located at the UI Research Park, is filled with an estimated $250 million worth of rock and soil samples collected during the drilling of roughly 40,000 borings across the state, mostly for water wells. The warehouse also contains unique rock, mineral, and fossil finds, including a septarian concretion (a mineral mass the size of a human baby with dragon scale–like markings) and lots of prehistoric marine fossils. Some of the rarest holdings in the IGS warehouse are rock samples from near Manson, Iowa, the site of a meteorite collision about 74 million years ago.

“Geologists can’t help but collect things. We’re hoarders,” says Clark, gesturing toward rows of shelves containing hundreds of boxed rock samples. “We have loads and loads of rocks.”

In Iowa, drilling companies collect rock and soil samples every 5 feet when sinking a new well. Those companies send the samples to the IGS for examination and storage. Some of the samples are in the form of long, cylindrical shafts called cores, which are extracted with hollow drill bits.

Other samples are in the form of crushed rock. These samples are extracted with rotary bits, which chew their way through soil and stone. Crushed rock samples are kept in small cloth sacks until an IGS geologist can examine them under a microscope. The warehouse stores dozens of large wooden crates full of such sacks, each representing a unique goody bag of Iowa geology.

Clark and other geologists record the information gleaned from the samples on strips of paper called strip logs. The deeper the well, the longer the strip log. Geologists use color codes, as well as abbreviations and symbols, to note the exact type of geological material encountered in the well. They then use this information to create geological maps, which allow well drillers, mining companies, farmers, developers, community planners, and others to understand exactly what lies beneath their feet.

Is it limestone or shale? Is there an aquifer? Maybe a sinkhole?

“These are important questions that must be answered before we decide how best to use our natural resources,” says Clark.

Of the 40,000 rock samples in the IGS warehouse, only about half have been studied and recorded, a backlog created by the pace of drilling in Iowa (the IGS estimates there are about 80,000 wells total) and a dearth of geologists to process and study them. The oldest samples date back to the 1870s. The deepest was extracted 18,560 feet below the Earth’s surface during an oil exploration project in 1987. Although the well has been vigorously studied, Clark is still working on the strip log.

“I think I’m going on five years now,” he says, pointing toward a stack of dusty sample boxes that he still has to review.

One of Clark’s favorite core samples is from the Manson Impact Structure, the site of a meteorite collision. It’s one of the sites that gets the most research attention, he says, with academics from around the world studying its samples in the hope of discovering a new bit of wisdom about Earth’s dynamic evolution.

When Clark pulls a Manson sample from its storage box, the cylindrical shaft of rock shines in the soft light as if it’s been polished. He explains that the extreme heat and pressure of the meteorite’s impact literally fused rock fragments together in a matrix of glass. Suspended inside the greenish glass are shards of bedrock of all shapes and sizes—a veritable fruitcake of geological samples that gives scientists a glimpse at the many layers of rock that make up our planet.

“When the meteorite hit, it caused a massive explosion that churned up all sorts of different rocks, lifting them up inside the central peak of the crater,” Clark says. “These are rocks we usually don’t get to see because they are buried so deep beneath the surface.”

This summer, core samples such as the one from the Manson Impact Structure are being photographed and logged by UI students to create an online GeoCore database. The digital database will complement the warehouse, a repository of the local geological past that’s shaping Iowa’s future.

“People ask me why we need to save these rocks,” Clark says, “and I tell them it’s because these rocks tell important stories about the place where we live, about the resources hidden underground, and the aquifers that provide us water.”

Iowa’s main aquifer, the Jordan Aquifer, is so large it stretches across roughly 90 percent of the state. According to Clark, it provides the majority of Iowa’s drinking water.

“The subsurface information we collect, study, and archive can help decision-makers protect this resource so that it will continue to sustain Iowa well into the future,” Clark says.