Natural Bridge EarthCache
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Nine miles north of Prospect, Oregon and one mile west of Union Creek in the Rogue River National Forest on State Hwy 62 is the entrance to The Natural Bridge Geologic Area and Natural Bridge Campground. The listed coordinates will bring you to the parking area for The Natural Bridge Interpretive Trail. The coordinates are close to the trailhead and interpretive signs.
Follow the trail from the trailhead for a short easy hike across and along the Rogue River to view the Natural Bridge. At Natural Bridge the Rogue River cuts its way through a 1.25 million year old lava flow and disappears underground at one point to come gushing to the surface again about 200 feet downstream.
Today the Natural Bridge is fenced off to protect the public and the resource. When I first came to the Rogue Valley I remember walking across the river on the basalt of the Natural Bridge. I could feel the water vibrating under the rock under my feet. Forest Service historians say the feature served as a footbridge for early settlers. Today, in early spring to late June there may be enough runoff to flow over the feature.
Most Natural Bridges are formed by erosion in sandstone or limestone. Examples of this type of bridge can be found in Arches National Park near Moab, Utah. What is happening here at this Natural Bridge is the Rogue River is flowing into and down a Lava Tube. Lava flows downhill with gravity. Lava Tubes form when the lava flow's surface cools and becomes solid rock. The molten lava under this crust continues to flow forming a tube. The molten lava drains from the tube leaving a tunnel. Here at this location the river has chosen to flow through one of these tunnels. Before it was fenced off one could cross the river by walking on the solid roof of the tunnel.
The requirements for logging this cache are to email me the answers to two questions: 1. Tell me if the Rogue River is flowing into the tube or over the Natural Bridge when you visited the site. 2. On the Interpretive Display near the coordinates the Forest Service tells you that the Natural Bridge was formed by two rivers. Tell me exactly what the sign says those two rivers were.
As always photos of your visit are appreciated.
If you would like to see more Lava Tubes visit Lava Beds National Monument about 30 miles south of Tulelake, California. At Lava Beds you can hike through the tubes.
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