Fort Rock
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| Fort Rock | |
|---|---|
 Aerial view of Fort Rock from the northeast. |
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| Elevation | 4,695 ft (1,431 m) |
| Location | Oregon, USA |
| Range | Basin and Range |
| Prominence | 345 ft (105 m) |
| Coordinates | |
| Topo map | USGS Fort Rock and Cabin Lake |
| Type | Tuff ring |
| Age of rock | 50,000 to 100,000 years |
| First ascent | prehistoric Native American |
| Easiest route | trail |
Fort Rock is a volcanic landmark called a tuff ring, located on an Ice age lake bed in north Lake County, Oregon, United States.[1] The ring is about 1/3 of a mile (0.5 km) in diameter and stands about 360 ft (110 m) high above the surrounding plain. Its tall, straight sides resemble the palisades of a fort, thus giving the rock its name. This region contains about 40 such tuff rings and maars and is located in the Brothers Fault Zone of central Oregon's Great Basin. On June 20, 1925, the Bend Bulletin wrote that Fort Rock was named by William Sullivan, an early resident.[2]
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[edit] Geology
Fort Rock was created when basalt magma rose to the surface and encountered the wet muds of a lake bottom. Powered by a jet of steam, molten basalt was blown into the air, creating a fountain of hot lava particles and frothy ash. The pieces and blobs of hot lava and ash rained down around the vent and formed a saucer-shaped ring of volcanic ash sitting like an island in the lake waters. Waves from the lake waters eroded the outside of the ring, cutting the steep cliffs into terraces.[citation needed]
The wave-cut terraces on the south side of the ring mark former lake levels of this now-dry lakebed. Southerly winds, which are still predominant in this region, apparently drove waves against the south side of the ring, eroding the soft ash layers, breaching it, and creating a large opening on the south side.
[edit] Age estimates
Previous age estimates of Fort Rock ranged upwards to 1.8 million years. Recently, the age of Fort Rock has been estimated at 50,000 to 100,000 years. This coincides with a period of time when large pluvial lakes filled the valleys of central Oregon and much of the Great Basin of the western United States. At its maximum, the water in Fort Rock Lake was estimated to cover nearly 900 square miles (2,330 square kilometers) and was about 150 feet (46 m) deep where the Fort Rock tuff ring formed.
The extensive terrace on the side of Fort Rock marks one lakeshore about 14,000 years ago. Even higher water levels are recorded on the tuff cliffs and at one point only the tops of the tuff ring were exposed as rocky islands in this inland sea. An age of about 21,000 years ago has been found for this highest lake level.[citation needed]
[edit] Designation
Fort Rock is designated as Fort Rock State Natural Area.[3] (formerly Fort Rock State Park)[4] Camping is not permitted. There is day-use with hiking trails, interpretive signs, restrooms, picnic tables, and a seasonal park host on hand to answer questions.
[edit] Other geological features
A nearby tuff ring has a water-formed cave, called Fort Rock Cave, where in 1936 Dr. Luther Cressman from the University of Oregon discovered sagebrush sandals and human artifacts dated approximately 9,000 - 10,000 years ago.[5][6] Entry to the cave is by prearranged tour only.
Hole-in-the-Ground and Big Hole are two nearby maars nearly one mile in diameter formed by steam explosion. They resemble impact craters formed by meteorites, but lack the heavy metal signature residues of space objects.
Crack in the Ground[7] and Fossil Lake[8] are two more nearby Ice Age geological features.
Fort Rock Village Historical Homestead Museum[9] and the small community of Fort Rock are one mile south of Fort Rock State Natural Area. The museum consists of an office/interpretive center/gift shop and is among a collection of historic buildings from north Lake County.[10] They offer tours from Memorial Day to Labor Day.
[edit] References
- ^ Fort Rock. America's Byways. Retrieved on 2006-08-06.
- ^ McArthur, Lewis A.; Lewis L. McArthur [1928] (2003). Oregon Geographic Names, Seventh Edition, Portland, Oregon: Oregon Historical Society Press. ISBN 0-87595-277-1 (trade paperback), ISBN 0-87595-278-X (hardcover).
- ^ Fort Rock State Natural Area, Oregon. PlanetWare. Retrieved on 2006-06-09.
- ^ Fort Rock State Park. Retrieved on 2006-06-09.
- ^ World's Oldest Shoes. University of Oregon. Retrieved on 2007-04-09.
- ^ Tucker, Kathy (2002). Fort Rock Sandals. Oregon Historical Society. Retrieved on 2007-04-09.
- ^ Crack-in-the-Ground. Trails.com. Retrieved on 2006-06-08.
- ^ Southern Oregon: Outback Scenic Byway. Oregon.com. Retrieved on 2006-06-09.
- ^ Homestead Village Museum, OR. America's Byways. Retrieved on 2006-06-09.
- ^ Fort Rock Museum. Fort Rock Valley Historical Association. Retrieved on 2006-06-08.
[edit] Bibliography
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This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations. |
- E.M. Bishop, C. 2004 "Hiking Oregon's Geology." The Mountaineers Books, Seattle, WA.
- Alt, David D. and Hyndman Donald W., Roadside Geology of Oregon, Mountain Press, Montana, 1998. ISBN 0878420630
[edit] External links
- Fort Rock is at coordinates Coordinates:
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