Set In Stone: Finding Fossils On The Trail

Sunlight filtering through the trees spotlighted an odd chunk of gray limestone on the Rough Trail in Kentucky’s Daniel Boone National Forest. Unusual-looking rings pocked the rock’s surface. I peered closely at it. The entire rock looked like a bowl of buttons compressed into stone. Then it hit me: This wasn’t an ordinary hunk of rock; it was a crinoid, an example of

native Kentucky fauna entombed in rock.

Finding fossils brings ancient history to life and makes a routine hike feel like a stroll through Jurassic Park. The remains of plants and animals buried millions of years ago can reveal how life evolved, what strange shrubs grew alongside today’s trail, and whether dinosaurs patrolled the land. The fossil of the flowerlike crinoid, for example, indicated that the Rough Trail was under an ocean 330 million years ago. “The crinoid would stick out its feathery pinnules to get plankton drifting by, then ease the food to its mouth,” explains John David McFarland, the Arkansas Geological Commission’s paleontologist and a fan of hiking fossil trails.

To be a successful amateur paleontologist, you need to understand the terrain. For instance, fossils exist only in sedimentary rock-layers of sediment that preserved plants and animals and then were compacted into rock. Arizona’s Grand Canyon, a mecca of sedimentary rock layers, is home to countless fossils. On the other hand, the volcanic rock common in California’s Sierra Nevada and Washington’s Cascades won’t yield a single relic.

Since sedimentary rock covers 75 percent of the Earth’s surface, any hike will likely lead you past the three most-fossiliferous types:

• Limestone can be any color, but is usually gray. Most limestone is actually a conglomeration of fossil fragments, but you may need a microscope to see them. Look at steep, weather-beaten slopes and cliffs like those in the Appalachian or Ozark Mountains to see exposed fossils.
• Sandstone can be any color, though iron oxide often colors it reddish brown, and it’s rough, like sandpaper. Sandstone is sometimes layered between limestone deposits in mountain slopes, and it’s prevalent in the desert Southwest.
• Shale is usually black or dark-colored, and flakes easily with a scratch of a fingernail. The badlands of the northern plains and ancient dry lakebeds of the West are examples of areas where soft shale is exposed.

Before making a trip to a fossil-rich area, consult guidebooks like those in Falcon’s Rockhounding series (888-249-7586; $12.95 each) or Mountain Press’s Roadside Geology series (800-234-5308; $12 to $20 each); all are available at www.backpacker.com/bookstore. You can also get maps that show bedrock types and ages from the state’s geological commission or the U.S. Geological Survey (see Resources on page 31).

Field guides to fossils, such as the National Audubon Society Field Guide to North American Fossils, by Ida Thompson (Alfred A. Knopf, 800-733-3000; www.backpacker.com/bookstore; $19), help match prehistoric creatures to bedrock age or type. In preparation for your hunt, train your eyes to spot specific shapes in the field by studying specimens at visitor centers, museums, or rock shops.

“When you’re looking for (particular) fossils, you should know the age of the rock” that will house the fossil, says Vincent Santucci, chief ranger and paleontologist for Fossil Butte National Monument, Wyoming. “Over the past 600 million years, many different creatures have come and gone. If you’re looking for dinosaurs, don’t look in beds that have trilobites, because they didn’t coexist.”

On the trail, look for exposed bedrock, like rock outcrops or bluffs. “Rock layers sometimes fall from these overhanging roofs, creating fresh surfaces to search for fossils,” says McFarland. “Another good place to look is where streams run directly over bedrock, such as at cutbanks. The stream polishes the rock to show more detail than you can see in rock that’s just exposed to weather.”

Since 90 percent of known fossils are marine animals, forget about looking for a T. rex skeleton and look instead for sea-dwellers like the trilobite, which is to invertebrate fossil hunting what the grizzly is to wildlife watching-what everyone wants to see. These buglike critters (arthropods, actually, that vanished 225 million years ago) resemble a matchbox-size horseshoe crab and are one of the few fossil types in which the body tends to stay articulated.

If a trilobite is the invertebrate grizzly, then the crinoid, or sea lily, is the oh-so-common rabbit. The “buttons” you see imprinted in rocks are the crinoids’ bases, which they used to anchor themselves to the seafloor. The crinoid’s arms, which resembled flowers, were rarely preserved.

Another common find is the brachiopod, whose fossilized remains resemble a mold of a thickly ridged mussel in rock. These 1 1/2-inch bivalve (two-shelled) organisms attached themselves to ancient sea bottoms 550 million years ago.

Just as scat and tracks provide a glimpse into the lives of today’s animals, fossils reveal the activities of the ancients. Dinosaur tracks may show a migration route and coprolites shed light on an animal’s ecology by recording what came out the other end after a meal.

When you do chance upon a fossil, look, but definitely don’t touch. Every rock packed out, from little Joey’s souvenir to the 12 tons of fossilized wood poached from Arizona’s Petrified Forest National Park every year, removes important historical and environmental information. And, points out Santucci, “fossils are nonrenewable.”

Besides, the best part of fossil hunting involves not plundering, but pondering. Says paleontologist McFarland, “Contemplate that life connection between you and some animal that lived hundreds of millions of years ago. It’s a way of putting yourself and life in perspective.”

RESOURCES

American Association of Petroleum Geologists Geological Highway maps. Eleven regional maps note some fossil locations. Contact: (800) 364-2274; http://bookstore.aapg.org; $12 each.

The U.S. Geologic Survey’s (USGS) two-sheet Geologic Map of the United States is available for $14 (888-ASK-USGS; http://ask.usgs.gov), and state geologic maps are $7 per sheet (http://geology.er.usgs.gov/eastern/stgeomap.html). The National Atlas at www.nationalatlas.gov, lets you create and download a map of any area of the country at the scale you want. Click on Make Maps, then select Geologic Map. Click on the Legend button below the map to see what color on the map represents each rock type.

Loriee Evans escapes to the backcountry outside her St. Louis, Missouri, home to “watch” ancient wildlife.