Get out of town and learn about Round Top, Oakland’s own volcano, with an EarthCache. All photos by Andrew Alden.The 21st-century sport of geocaching is providing a new way to teach and learn about geology. Geocaching prompts people sitting at a computer to do what our parents always urged—go out and play. And a new twist in the game replaces the traditional payoff of choosing a trinket from a hidden stash with a short personal lecture on the rocks at your feet or the landscape around you. This type of geocache is called an EarthCache.

By now you must have heard of geocaching, the self-guided sport that takes players into the great outdoors by combining GPS wayfinding technology with geographic clues on the web. In the basic game, you get the location of a hidden box on a geocaching website—just a latitude and longitude. Using your GPS unit, you make your way to that spot, find the container and score a point by recording the achievement.

This is a good way to have fun in the outdoors with a minimum of rules and structure. Millions of people have played, and more than a million geocaches are registered around the world.

The first time I was exposed to geocaching was in 2004: I was out to explore the southern Diablo Range, and my friend came along to find some caches there.

A geocache in an ammo box lurks in a boulder pile; a logbook and assorted trinkets are inside.

He found his first cache of the day in a boulder pile, a place with a superb view of the inner Coast Range. He opened the box, traded one of his trinkets for another, and left his name in the logbook. Then we sat and talked about what we were seeing in front of us.

Concretions and tafoni in the southern Diablo Range.

I showed him concretions sticking out of sandstone beds; we poked our heads through the large erosional holes called tafoni. We photographed old smelting works, collected a few stones, visited a mineral dealer at home, lunched on the porch of an abandoned house.

That’s the way to learn about geology. A ramble along a path or roadside in the company of a teacher is the best way to learn, but such a thing can be hard to arrange. I’ve done that kind of teaching to groups—it’s fun and rewarding and a lot of work. An EarthCache is the next best thing: instead of finding a hidden box, you just show up. And instead of trading trinkets, you read a lesson about what’s in front of you.

There are more than 10,000 EarthCaches listed on the EarthCache website. Each one has a geology lesson associated with it approved by the Geological Society of America, plus a task you must perform to prove that you visited. You email your proof to the EarthCache site, and that’s what it’s all about.

A few EarthCaches in the Bay area:

Round Top, Oakland (shown here)
South of Fort Funston, San Francisco
View from Windy Hill, San Mateo Peninsula
Volcanic rocks of the Pinnacles
Marine terraces in Santa Cruz
Point Reyes earthquake trail

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EarthCaches: Learning Through Hide-and-Seek 12 June,2013Andrew Alden


Andrew Alden

Andrew Alden earned his geology degree at the University of New Hampshire and moved back to the Bay Area to work at the U.S. Geological Survey for six years. He has written on geology for since its founding in 1997. In 2007, he started the Oakland Geology blog, which won recognition as "Best of the East Bay" from the East Bay Express in 2010. In writing about geology in the Bay Area and surroundings, he hopes to share some of the useful and pleasurable insights that geologists give us—not just facts about the deep past, but an attitude that might be called the deep present.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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