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Geologists love field trips. They'll travel thousands of miles to explore rich geological sites such as the Grand Canyon of the United States or the Great Rift Valley of Africa. In these locales, earth and rocks from many different eras lie exposed, laid down in strata, like pages in a book.

It's unlikely that you'll find anything so geologically rich in your own backyard, but the typical backyard is by no means barren of significance. It will reveal to you much about the forces and processes which have created the plot of land upon which you have built your home.

A pile of rocks and "soil" samples gathered from one small plot of land became the treasured return cargo of the Apollo 11 moon mission in 1969. The area over which the astronauts collected these samples was very restricted - not much larger than a good sized backyard. Yet the samples answered many fundamental questions about the moon's origin and history. The rocks were overwhelmingly of volcanic origin, had no significant organic content, and lacked the water content found in Earth's rocks. The public was somewhat disappointed that the rocks looked so ordinary, yet they answered many questions that had excited the curiosities of scientists for centuries.

Similarly, you're unlikely to come across rocks of great rarity in your backyard, but if you're willing to do a little digging (both physically and through research), you'll discover much about what's been going on in your backyard over the centuries, millennia, and even millions of years before you moved there.

Digging is usually necessary because the surface of your back yard may have been affected by the original site preparation work when your house was built or by subsequent landscaping. Many of the native rocks and boulders may have been removed, and new soil may have been trucked in to support gardening. If you dig down a foot or more, you'll more likely find naturally deposited rocks and soil. By no means is this foolproof, however. While at college, I was surprised to learn that the entire area surrounding my campus was originally built atop sand dunes. I didn't have a clue until I read about it.

Keep samples of the dirt and the rocks that you find beneath your yard's surface. Both rocks and dirt can be classified into three basic types, so it's easy to get started. But there's plenty of room to advance your studies, because each classification system, with its sub-classifications and combinations, gets more complicated the closer you look and

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