From a more technical perspective, the two are very different.
This is from wikipedia:
Distinct
geomorphological features include coulees,
dry falls, streamlined hills and islands of remnant loess, gravel fans and
bars, and
giant current ripples.
[7]
The term scabland refers to an area that has experienced fluvial erosion resulting in the loss of
loess and other soils, leaving the land barren.
[9] River valleys formed by erosional downcutting of rivers create V-shaped valleys, while
glaciers carve out
U-shaped valleys. The Channeled Scablands have a rectangular cross section, with flat plateaus and steep canyon sides, and are spread over immense areas of
eastern Washington. The morphology of the scablands is butte-and-basin.
[9] The area that encompasses the Scablands has been estimated between 1,500 and 2,000 square miles (3,900 and 5,200 km2), though those estimates still may be too conservative.
[10]
They exhibit a unique
drainage pattern that appears to have an entrance in the northeast and an exit in the southwest. The
Cordilleran Ice Sheet dammed up Glacial Lake Missoula at the Purcell Trench Lobe.
[10] A series of floods occurring over the period of 18,000 and 13,000 years ago swept over the landscape when the ice dam broke. The eroded channels also show an
anastomosing, or braided, appearance.
The presence of
Middle and
Early Pleistocene Missoula flood deposits have been documented within the Channeled Scabland as other parts of the Columbia Basin, e.g. the Othello Channels, Columbia River Gorge, Quincy Basin, Pasco Basin, and the
Walla Walla Valley. Based on the presence of multiple
interglacial calcretes interbedded with glaciofluvial flood deposits,
magnetostratigraphy,
optically stimulated luminescence dating, and
unconformity truncated
clastic dikes, it has been estimated that the oldest of these megafloods flowed through the Channel Scablands sometime before 1.5 million years ago. Because of the fragmentary nature of older glaciofluvial deposits, which have been largely removed by subsequent Missoula floods, the exact number of older Missoula floods, which are known as
Ancient Cataclysmic Floods, that occurred during the Pleistocene cannot be estimated with any confidence.
[3][4] As many as 100 separate, cataclysmic Ice Age floods may have occurred during the last glaciation.
[11] There have been at least 17 complete interglacial-glacial cycles since about 1.77 million years ago, and perhaps as many as 44 interglacial-glacial cycles since the beginning of the Pleistocene about 2.58 million years ago. Presuming a dozen (or more) floods were associated with each glaciation, the total number of cataclysmic Ice Age Missoula floods that flowed through the Channeled Scablands for the entire Pleistocene Epoch could possibly number in the hundreds, perhaps exceeding a thousand Ancient Cataclysmic Floods.
[5]
There are also immense
potholes and
ripple marks, much larger than those found on ordinary rivers. When these features were first studied, no known theories could explain their origin. The
giant current ripples are between 3.3 and 49.2 feet (1 and 15 m) high and are regularly spaced, relatively uniform hills.
[9] Vast volumes of flowing water would be required to produce ripple marks of this magnitude, as they are larger-scale versions of the ripple marks found on streambeds that are typically only centimeters high. Large potholes were formed by swirling vortexes of water called
kolks scouring and plucking out the bedrock.
[10]
The Scablands are littered with large boulders called
glacial erratics that rafted on glaciers and were deposited by the glacial outburst flooding. The lithology of erratics usually does not match the rock type that surrounds it, as they are often carried very far from their origin.
[10]
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If you read the above, you will see a lot of jargon about glacial features, erratics, drop stones, gravel fans and bars, ripples, braided channels witha rectangular cross section etc.
These are specific qualities condensed into superpositionally shallow strata.
Whereas with the grand canyon, you have a vast array of varying rock types and formations and unconformities and biostratigraphic features etc. For example, you will find countless cyclothems throughout the grand canyon. You will find trans and regressive features, rocks of sand, silt, clay, various forms of carbonaceous rocks, varying types of minerals and metamophic features. Unique structural compressional features etc.
You can find many many things in the grand canyon that you couldnt find in the scab lands, and vise versa.
So, you can say all you want that they look the same, but to anyone who is actually knowledgeable of what is out there, it is quite clear that they are very different.
