Geocaching is a new form of treasure hunting using a GPS receiver and a map to locate treasure caches throughout the globe. There are hundreds of caches in northern California alone. It's a lot of fun and its growing quickly in popularity. It's also great fun for kids.

How Does It Work?

The idea is very simple. You need a GPS receiver, a map, and a small item to exchange when you find the cache. You load the latitude/longitude coordinates of the cache into your GPS receiver and navigate your way to find the cache, typically some sort of water-tight container like a Tupperware box or an old army ammo box. Inside you'll find a collection of items other people have left behind in exchange for items they took. You'll also find a log book and a pencil so you can log the date and time you found the cache, as well as any comments you want to make.

The items range broadly, but kitch is big: key chains, troll dolls, squeek toys, squirt guns, bobbleheads, 3d glasses, discount coupons, etc. Sometimes you'll find small calculators, even a cell phone, or other small electronics, a set of allen wrenches or a bicycle tube patch kit. You get the idea. Bring something comparable to exchange.

Finding something like a small, hidden Tupperware container using a GPS receiver when you already have the coordinates is not as easy as it may sound. You could be standing at a trailhead with one trail leading off one way and a second trail leading off another, and your GPS receiver pointing you between them. Which way do you go? Also, once you start to get close to the cache, say within a couple hundred feet, GPS accuracy starts to play a role. As you get closer and closer, you have to pay less attention to the GPS receiver and more attention to the surroundings. You have to think, if I had hidden this cache, where would I have hidden it?

Caches can be hidden in places that can be physically difficult to reach. Some require a strenuous hike, others may require a bit of rock climbing. Some can only be reached at low tide. Most, however, are easy to get to. Hiding caches in places that require people to make their way far off a trail is frowned upon, so most caches are within a few yards of a trail.

Get a list of caches for Muir Woods, Mt. Tamalpais, GGNRA from http://www.geocaching.com/.

Get a list of caches for Muir Woods, Mt. Tamalpais, GGNRA from http://www.navicache.com/.