Hi-tech hiking with the National Parks Service
The article is primarily about GPS and hiking, but at the end, the following, of course using “digging up ground” in the description 
is included:
Another relatively new recreational hiking activity that will be discussed at the GPS seminar will be geocaching-a hide-and-seek type game for GPS users. The basic idea for geocaching is to have individuals and organizations set up caches all over the world, post the coordinates online, typically on the Web site www.geocaching.com, and then let treasure hunters track down what has been stashed.
Neal Oren, manager for the Adventure 16 store in Tarzana, said geocaching has slowly developed into a popular outdoors activity over the last several years. He estimates that one in 10 hikers currently own a GPS unit, which range in price from $100 for low-end models to more than $700 for units that come as small as a watch or with built-in communication features.
“It’s a great way for families to get their kids outdoors and interested in hiking,” Oren said of geocaching. “People seem to really like the treasure hunting aspect of it.”
However, Elliott warns that there are certain wildlife areas that are not to be utilized by geocachers because they sometimes fall under protected status. Because a typical geocache can involve digging up ground to burying some form of treasure, Elliott said he would discuss the proper areas, situations and techniques for locating a geocaching spot that would prevent adverse environmental effects.