In 2000, Dave Ulmer of Portland, OR, put out a cache of "treasure" and challenged the public to find it using GPS technology. With guidance from GPS super-compasses (costing $75-$1000), the hunt was on. Now geocaching has become a hot hobby across the U.S. and the world.There are about 430,000 caches hidden all over the globe. Some, the size of postage stamps, contain only tiny logbooks that successful scavengers sign with their "eureka." Caches rural areas can be quite a bit larger and still remain inconspicuous; these may contain trinkets or even cash prizes (the rule is: take out a souvenir, and leave one behind, too). The website http://www.geocaching .com is one place to start.Karina Bland's feature story for the Arizona Republic gives a tantalizing flavor of this craze. "It was like I was a kid again, finding that treasure," said Ed Schraut of Sun City. He found a trunk near the Vulture Mine, near Wickenburg, AZ, containing eye patches, bandanas and plastic pieces of eight. Gay Griebach reports that the Chamber of Commerce in West Bend, Wisconsin, calls its town geocache capitol of the Midwest, boasting "450 caches within a 7-mile radius."   It sounds like an ideal combination of road rally and scavenger hunt — Perfect for garage-sale fans who love the outdoors and would just as soon not buy anything.