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Lower Grand Coulee, Talus Slopes and Steamboat Rock
Key to Mile Markers and Highways Notation |
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| Trip Mileage | Mile Marker | Highway |
| 1.3 | MM 282 | US 2 |
(Washington State Parks map)
Leaving Coulee City, we head east on US 2 for a few minutes to the junction with State Highway 155 North. We are following the winding path of the Lower Grand Coulee to the town of Grand Coulee.
Click image for a larger map of this leg of our trip up Banks Lake.
[121.2 MM 192]
We are at the junction of Highway US 2 with State Highway 155 North. Staying to the left on 155N, we continue up Grand Coulee. At mile marker 2, we will cross the Coulee Monocline.
As we travel the edge of the coulee, you might imagine you are on Mars in the Nanedi Vallis area. This channel might have been carved by water but it is not certain. An unanswered question is: If this was caused by a river or a flood, where did all the water go?
Click on image for a detail view.
Here is part of the caption for the photo:
"It shows the canyon of Nanedi Vallis, one of the Martian valley systems cutting through cratered plains in the Xanthe Terra region of Mars. The picture covers an area 9.8 km by 18.5 km (6.1 mi by 11.5 mi), and features as small as 12 m (39 ft) can be seen. The canyon is about 2.5 km (1.6 mi) wide. Rocky outcrops are found along the upper canyon walls; weathered debris is found on the lower canyon slopes and along the canyon floor. The origin of this canyon is enigmatic: some features, such as terraces within the canyon (as seen near the top of the frame) and the small 200 m (660 ft) wide channel (also seen near the top of the frame) suggest continual fluid flow and downcutting. Other features, such as the lack of a contributing pattern of smaller channels on the surface surrounding the canyon, box-headed tributaries, and the size and tightness of the apparent meanders (as seen, for example, in the Viking image 89A32), suggest formation by collapse. It is likely that both continual flow and collapse have been responsible for the canyon as it now appears."
Photo Credit: NASA/JPL/Malin Space Science Systems
[123.8 MM 3 State 155N]
This view across the lake shows the columns and layers of basalt on the west side cliffs. You can see several layers of columnar basalt. Click on the image or here to get a
detail view. The foreground field is the top of the east cliffs with Banks Lake out of sight below. Note at the base of the cliffs the basalt talus; the pile of rocks and boulders broken away by weathering. When water seeps into the cracks of the rock and freezes, the expanding ice breaks away pieces of the basalt. This weathering erosion happens to all exposed rocks of any kind.
Layers of basalt on the west side cliffs.
Click on image for a detail view.
[126.7 MM 6]
In the road cuts all around are basalt layers. Some columns are twisted like claws and bowed like reaching fingers.
[131.1 MM 10]
To our right we can see talus slopes with huge boulders eroded from the east side cliffs. The larger boulders are as big as a van or small truck.
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Geology Terms
Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Basalt
- Volcanic rock caused by partial melting of the Earth's crust.
- Channeled Scabland
- Area in Washington state where huge floods made channels in a large, deep basalt flow. Named by J Harlan Bretz during the 1920's in various publications. See also Channeled Scabland and Glacial Lake Missoula.
- Coulee
- Long winding channel cut through lava formations. A term primarily used in the northwestern United States.
- Erosion
- Lifting and removal of rock, dirt, sand and the like caused by wind, water, or glacial ice.
- Gneiss
- A type of metamorphic rock formed as older rocks recrystallize under heat and stress from pressure chactorized by a layering of light and dark bands or streaks.
- Granite
- Coarse-grained igneous rock usually without obvious bands or markings.
- Schist
- A type of metamorphic rock formed as older rocks recrystallize under heat and stress from pressure charactorized by a flaky layering of light and dark areas.
- Talus
- Rock debris that has fallen from the sides of a cliff or steep slope.
Kids' Cosmos… Expanding Minds Beyond the Limits of the Universe
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