Ice Age Floods Features - East Rim of the Grand Coulee

Photos from a September hike along the east rim of the Grand Coulee - between the "Million Dollar Mile" and Northrup Canyon. Bruce Bjornstad and I enjoyed the awesome Ice Age Floods features found along this 15 mile hike. Not sure of ownership in a few areas ... we tried to stay as close to the rim as possible throughout the hike.

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Million Dollar Mile
This spendy one mile stretch of Hwy 155 in the Grand Coulee was built in 1948. The cut through the basalt became necessary as the Bureau of Reclamation filled Banks Lake.


Hiked from location marked as 7 to 4.
The Grand Coulee is considered by many to be the most remarkable legacy of the Ice Age floods. Today the massive coulee is used for off-channel storage of Columbia River water. A huge pumping station adjacent to Grand Coulee dam lifts water into the coulee. This water will either generate power as it returns to the Columbia River or flow south to irrigate crops in the Columbia Basin Irrigation Project as far south as Pasco.

1. Lake Roosevelt
2. Grand Coulee Dam
3. North Dam
4. Northrup Canyon
5. Steamboat Rock
6. Nespelem Silt deposits (white bank)
7. Million Dollar Mile
8. Dry Falls Dam
9. Dry Falls
10.Deep Lake


Geologist/Author Bruce Bjornstad hikes near an impressive basalt butte created by the Ice Age Floods.


Hiking south to north along the coulee rim.

The floods scoured out many saucer shaped potholes along the east rim. These are cool but I'm more impressed with the Deep Lake and East Lenore Channel potholes a few miles to the south. Bruce for scale.


The potholes hold water late into the season. A Google satellite image got us close to these potholes. We then followed animal trails to go from one pothole to the next.


The guy on the right - that didn't want to pose - looked like a nice buck.


Half of this pothole disappeared as the Grand Coulee widened.


Looking north up the Grand Coulee. Basalt knob on east rim shown in next image.



Photo by Bruce shows Steamboat Rock to the north. Tom hiking along rim at right.


This Bureau of Reclamation photo shows Grand Coulee Dam and the upper Grand Coulee.

1. Grand Coulee Dam
2. Lake Roosevelt
3. Pumping Station
4. Feeder Canal
5. North Dam
6. Steamboat Rock


Early photos show the Grand Coulee looked much different prior to the construction of Grand Coulee Dam. Photos from top show Steamboat Rock, BOR employees walking through wheat fields on the coulee floor and the clearing of sagebrush.

To view hundreds of photos taken during the construction of Grand Coulee Dam and the Columbia Basin Irrigation Project, visit Central Washington University's Rufus Woods Collection.

This band of palagonite formed when lava flowed into water. -Photo by Bruce ...Tom trying not to slip on the mini marbles.

Columbia River Basalt Group


Bruce standing on ring dike near the coulee rim.



Google satellite view of the same ring dike.
-Use your mouse to navigate satellite view-


East coulee wall
1. Hwy 155
2. Steamboat Rock State Park entrance
3. Northrup Canyon


Here's a shot for the three or four people out there who enjoy longitudinal groove images.


Looking north to Castle Rock (flat top).


Steamboat Rock in the upper Grand Coulee. The Nespelem Silt deposits on the coulee floor can be examined along the lake shore.


The white banks below Steamboat Rock sure are interesting. This view from the coulee rim shows the best exposure of Nespelem Silt in the coulee. These lake deposits were probably laid down in Glacial Lake Columbia between (or after) the megafloods.


Wave action along the shore of Banks Lake disturbs the silt deposits.


Here are a couple of shots taken during a visit to the Nespelem silt deposits in the spring. The petrified doughnuts found on the beach make me hungry.


Bruce views a section of the Nespelem silt deposits. The bank is unstable in places ... Use caution if you explore this area ... Not a good place to visit with children!!!


In some sections of the Nespelem silt deposits you can follow the alligator skin pattern into the bank. Ice age mud cracks!




Back to the coulee rim hike ... Another shot of the Nespelem silt deposits. The white banks shown in previous images are along the far shoreline in this photo. Note the giant current ripples.


Bruce views the flood-swept east rim of the Grand Coulee.

Map created by Bruce shows ice lobe that diverted Columbia River and floodwaters from Glacial Lake Missoula down the Grand Coulee.

At times the ice lobe blocked the Columbia River creating Glacial Lake Columbia. This photo from another trip (a few miles NE of Northrup Canyon) shows Glacial Lake Columbia shorelines cut into the hills 1,000 feet above the surface of Lake Roosevelt.


Haystack Rocks (large pieces of basalt) scattered above the west rim of the Grand Coulee were left behind when the ice sheet melted.


Here's a shot of a huge haystack rock west of the Grand Coulee (wife Teresa left of rock). Yeager Rock sits next to Hwy 172 east of Mansfield.


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Tough place to farm! That's Yeager rock upper left. Use mouse to view more debis left by the ice sheet.


One of the erratic boulders stranded on the east rim of the Grand Coulee. Not as many granite boulders on the east rim compared to what you find on top of Steamboat Rock.


Photo from another hike shows one of the many granite boulders stranded on top of Steamboat Rock. View down the Grand Coulee.


Another of the large erratics on top of Steamboat Rock. View shows mouth of Northrup Canyon (1) and Whitney Canyon (2) along east rim.


Northrup Canyon from Steamboat Rock. Plenty of history in this canyon.


Northrup Canyon Structures.

It was getting pretty late when Bruce and I reached Northrup Canyon. Great day with perfect weather.

Open link to view map of Coulee Corridor


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