Lake Missoula: Thompson Falls to Spokane

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Acknowledgement

I need to make it crystal clear that none of this is my own research. Thepictures on this and associated pages were taken on a GSA field trip in 2003 ledby Norm Smyers of the U. S. Forest Service and Roy Breckenridge of the Idaho Geological Survey, and the interpretationspresented here are largely those of Dr. Smyers and Dr. Breckenridge as presented on the field trip andits guidebook. I thank Dr. Smyers and Dr. Breckenridge for an outstanding fieldexperience.

Thompson Falls

3.1 Beaver Creek

3.2 Cabinet Gorge Dam



	The gorge here is a miniature version of Devils Gate, Wyoming. The flat terrace across the river is not bedrock but glacial deposits. A bedrock spur projecting into the valley was buried and then incised by the river.

3.3 Lake Pend Oreille

Above: panorama of Lake Pend Oreille, from south at left through west(center) to north (at right). The Clark Fork River enters the lake out of viewto the left and the lake drains through the valley left of center, where amoraine impounds the lake. The distant hills left of center blocked the icelobe. The ice tongue that dammed Glacial Lake Missoula was no narrowsliver. It filled this entire valley and extended about halfway up the hills onthe left syline.

	Mouth of the Clark Fork River where it enters Lake Pend Oreille. The high peak at far left is Green Monarch, which calls to mind some sort of weird mutant butterfly. The notch just inside the picture was possibly an ice-marginal drainage.

3.5 Farragut State Park

	Why is a state park in Idaho named after an admiral? Because it used to be a Navy training center during World War II. The Navy still has a facility in nearby Sandpoint where they test equipment. The roads in the park have the characteristic look of a military base layout.

	The military has an unerring instinct for sand and gravel; in this case, a moraine. This is the moraine that impounds Lake Pend Oreille. It can be seen abutting the mountains at center. It's not that the military likes sand and gravel so much, but they tend to locate facilities on otherwise marginal and little used land.

Rathdrum Prairie

	Left and below: general views of Rathdrum Prairie.

Below: the grazing illumination nicely brings out current ripple marks on the Rathdrum Paririe.


	Closing the circle. The hill at right is the north side of Ross Point, the first stop on the trip.

Spokane Aquifer

	The flood gravels are very porous and serve as the principal aquifer for the Spokane area. This gravel pit extends below the water table but dredges continue to extract gravel from underwater.
	The very abundance of the Spokane aquifer means paradoxically that little is known about it. Most wells are shallow, so little is known of the depth or stratigraphy of the aquifer.

Created 9 November 2003, Last Update 07 June 2020