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Recommended by the Oregon Department of Geology and Mineral industries

Lake Owyhee, Malheur County
(photo courtesy Oregon Department of Transportation)


Lake Owyhee, created by a dam on the Owyhee River, offers boaters an extraordinary view of Miocene volcanism (about 15 million years ago). Ash from that time preserved plant and animal fossils that show a much wetter climate. Rhinoceroses lived next to ancestral horses, deer and antelope. The off-white ash layers, pinkish-gray rhyolite, and dark colored basalt create a colorful palette.

The Owyhee Uplands have been uplifted to more than 4,000 feet above sea level, and the resulting stream erosion has produced the deep, narrow, winding canyons seen in the area today. The Owyhee volcanic field includes several calderas, such as at Grassy Mountain and Mahogany Mountain, that are large collapse features better recognized by the distribution of specific types of volcanic rocks rather than by present day topography.

These same volcanic processes have been responsible for numerous gold occurrences which have been prospecting targets over the last few years. Typically, the gold occurs as microscopic particles that have been deposited by hot-spring systems. Portland State University graduate students often learn geologic mapping in this area (several theses have been written and abstracts published in Oregon Geology).

Access: From Interstate I–84 at Ontario south on State Highway 201 toward Adrian. Several roads branch off toward the west to Lake Owyhee State Park, which offers camping sites. Boat rentals are available in the area.




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Oregon Department of Geology and Mineral Industries
800 NE Oregon Street #28, Suite 965, Portland, OR 97232-2162
(971) 673-1555, FAX (971) 673-1562
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