We can thank Central Oregon's tumultuous volcanic history for most of the things we all love most about living here: the outdoor recreation, the beauty, and probably even the beer if you want to talk hydrology (but you probably don't, so...). One more gift bestowed upon us by virtue of tectonic mayhem? Rocks! Central Oregon is renowned by rock hounds worldwide for the volume and diversity of stones found here. Because of this, I can only tell you about these locations, for the actual directions you will need to purchase a map produced by the Prineville-Crook County Chamber of Commerce, U.S. Forest Service and the Bureau of Land Management, which also provides GPS coordinates. Maps are available in town at the Bend Visitor Center or through any of the agencies' websites.
Roughly 200 miles southeast of Bend, near the Hart Mountain National Antelope Refuge, sits some of the best rock hounding in the State. This site is known to possess agate, jasper and petrified wood. It's a four-hour drive from the city, but well worth it for the diverse array of stones that can be found here. Once down there, might as well make a proper trip of it and hit the hot springs as well.
Nestled in the Ochocos, just 30 miles northeast of Prineville, this site may well be the closest to Bend to find the infamous Oregon Thunder Egg. These tricky specimens are the Kinder Surprise of the rock-hounding world. Looking seldom more interesting than a dirt clod on the outside, once sawed open they may reveal themselves full of crystals of agate, jasper or calcite, or they may be completely hollow. The finding out is half the fun.