Field Trip to Mars

Digital Relief Map Text

Map of Eastern Washington The map at right by Ray Sterner, Johns Hopkins University shows the mountains and rivers (dark blue) of the area. The different colors indicate elevation and the red lines show state boundaries. Click here for a larger (75K) image or a full size (196K) image.

Here's the text that accompanies this image:

We see eastern Wash., Idaho panhandle, NW Mont., southern B.C. and a bit of NE Oregon. The Columbia Plateau (actually a basin), an area of some 5000' of Miocene basalt flows, dominates the plains part of the map and is surrounded on all sides by mountains.

The Snake River forms the border between Idaho/Oregon and Idaho/Wash. as far north as Lewiston, ID 46.4, 117.0 where it is joined by Clearwater River 46.1, 115.0 draining the rugged Precambrian terrain of the Idaho batholith along the SE side of the map. The Salmon River, a great whitewater rafting river, enters the map at 45.55, 115.0 flows through spectacular canyons of Precambrian metasediments and granite, turns north at Riggins 45.4, 116.3, past Whitebird 45.8, 116.3 where Whitebird Creek enters the Salmon. Continuing on down the lower Salmon through some nice rapids to where it enters the Snake at 45.9, 116.8 (It is great fun to roll over the side of your raft, with lifejacket on of course, and float the last rapids to the confluence with the Snake in the water! As you enter the Snake your body immediately feels the colder water coming out of the bottom of Hells Canyon Dam at 45.2, 116.7). This part of the Snake is famous for sturgeon fishing. At Clarkston, WA 46.4, 117.05 the Snake turns west, follows a winding course through Palouse country and enters the Columbia at 46. 2, 119.0.

The eastern plains (buff), roughly from the Palouse River 46.8, 118.0 northeast to Spokane 47.7, 117.4 and east into Idaho, is the Palouse country. This very fertile area is the high rolling hills, hummocky, dry-land wheat farming land that is under lain by as much as 200' of loess (wind-blown dust) deposits formed by the deflation of dry post-glacial plains to the west.

The mountains of southern B.C. and western Montana are largely granite and granodiorite batholiths of Cretaceous and younger age that, together with the Idaho batholith, intruded much older rocks known as the Belt Supergroup. These ancient rocks are a complex assemblage of metamorphics about 1.0 Ga that mark the western edge of the old North American continent.

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The valley in NE corner of the map is the Kootenay Valley bordered on the east by the McDonald/Salish Ranges and on the west by McGillivray Mts. Kootenay River flows south through this fertile valley, loops south into the U.S. through the Purcell Mts., past Bonners Ferry 48.7,116.4, on NW into Canada and into Kootenay Lake at 49.2, 116.6. The Clark Fork of the Flathead River enters the map at 47.55, 115.0, flows NW past Cabinet Mts. on the north and Bitterroot Range on the south to enter Pend Oreille Lake at 48.2, 116.2. The Pend Oreille River exits Lake Pend Oreille, continues north through the Selkirk Mts., loops north into Canada a bit and joins the Columbia river at the border 49.0, 117.6. Lower Arrow Lake is at 49.5, 118.1. Okanagan river flows out of Lake Okanagan 49.4, 119.6 to flow south into the Columbia river at Fort Okanagan 48.1, 119.7. The flat area between the Yakima and Columbia rivers at 46.75, 119.5 is the site of the Hanford Nuclear Site.

The folded/faulted basalt ridges entering the map from the west are: Horse Heaven Hills in the loop of the Yakima/Columbia rivers; Rattlesnake Hills along lat. 46.4; Umtanum Ridge between 46.5 and the Columbia; Saddle Mts. along lat. 46.8; Frenchman Hills along lat. 46.95 to the south side of Potholes Reservoir 47.0, 119.3.

The incised vallleys and intricate drainage channels that occur west of a NE-SW line from Spokane 47.7, 117.4 to the Columbia river are only slightly visible (in the yellow/buff area) in this 3D topographic rendition but are clearly visible on satellite imagery. This is the area of the Channeled Scablands of the Columbia Plateau, created by the world's greatest flood. J. Harlan Bretz studied the scablands in the 1920's and realized the bizarre erosional channels had to be caused by catastrophic water flow. Though he didn't know the source of the water, he named it the Spokane Flood. His ideas were received by his collegues with skepticism and mirth. Subsequent detailed study by other geologists has vindicated his theory and found the source of the water in northern Idaho and western Montana. During the glacial period, 16,000 yrs. ago, great ice sheets from the north flowed south to block and dam the Clark Fork river at Pend Oreille Lake. Glacial Lake Missoula was formed which reached its highest level at about 4350' elevation, was at least 2000' deep and contained at least 500 cu MILES of water. At the highest lake level the ice dam was floated and broke up with catastrophic results: the greatest flood of all time. The flooding was not once, but many times, evidenced by the 30 or more faint shoreline scars on the valley walls of the Clark Fork in western Montana, each scar the mark of a separate lake filling.

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What were the downstream effects?

A 2000' wall of water gushing out of the mountain foothills of ID/Mont.
Clark Fork and Flathead rivers carried 8-10 cu MILES of water per hour during peak glacial lake draining.
All drainages were completely filled with floodwater and channels were cut across divides;the channels, now dry, contain stream-rounded boulders several feet in diameter. The dry channels are now several hundred feet above modern drainage.
Scouring to fresh bedrock occurred everywhere; now-dry channels have fresh, unweathered vertical sides that appear to have been carved last week.
Scattered islands of loess, streamlined in the direction of flow and showing high water benches, remain as ships on a black basalt sea where all loess has been removed.
Giant ripple marks were left on the surface, identical to any ripple marks except size: they have a wavelength of several hundred feet and amplitudes of 30' or more.
The water backed up by basalt ridges formed a lake 1000' deep in the lower basalt plains and flowed out the Wallula Gap 46.0, 119.0 at the rate of 40 cu MILES per day during peak draining.
The Columbia Gorge backed water up to as much as 1000' during the day or so of maximum flood stage.
Imagine the flow through the Columbia Gorge where tributary streams were scoured back to create falls where they now enter the gorge. The gorge walls were scoured clean up to 1000' or so.
Water backed up to a depth of 400' in the Willamette Valley south of Portland (map to the west).
The unusual offshore bars of the mouth of the Columbia probably resulted from these floods.
All traces of Native Americal culture were scoured from the valleys or deeply buried in lee areas. Repeated catastrophic floods separated by periods of floral, faunal and cultural recovery is a fate hard to imagine in modern times.

The Wallowa Mts 45.2, 117.4 are drained by the Grande Ronde River which flows out of Blue Mts. (NE-SW range centered on 46.0, 117.9) at La Grande 45.3, 118.1. Grande Ronde flows east across the fertile La Grande Valley then turns north on the east side of the valley, flows north between Blue Mts. (west) and Willowa Mts. to intersect the Snake at the Idaho line 46.1, 116.95. The common boundary of Wash.,Oregon & Idaho is the general site of the Miocene volcano supplying the vast amounts of basalt to the Columbia Plateau.

(Lowell Bogart
Geological & Exploration Associates
P.O. Box 761
Port Townsend, WA 98368)

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