Olympic-Wallowa Lineament - Introduction To A Puzzle

Introduction To A Puzzle

Most geological features are initially identified or characterized from a local expression of that feature. The OWL was first identified as a perceptual effect, a pattern perceived by the human visual system in a broad field of many seemingly random elements. But is it real? Or just an optical illusion, such as the Kanizsa triangle (see image), where we "see" a triangle that does not really exist?

Raisz considered whether the OWL might be just a chance alignment of random elements, and geologists since have not been able to find any common unitary feature, nor identify any connection between the various local elements. Davis (1977) called it a "fictional structural element". Yet it has been found to be coincide with many faults and fault zones, and to delineate significant differences of geology. These are much too correlated to be dismissed as random alignments. But for all of its prominence, there is as yet no understanding of what the OWL is or how it came to be; it looms just beyond the horizon of current human knowledge.

The OWL piques the interest of geologically minded persons in part because its characteristic NW-SE angle of orientation – approximately 50 to 60 degrees west of north (a little short of northwest) – is shared by many other seeming local features across a broad swath of geography. Around Seattle these include strikingly parallel alignments at the south end of Lake Washington, the northside of Elliot Bay, the valley of the Ship Canal, the bluff along Interlaken Blvd. (aligned with the Ship Canal, but offset slightly to the north), the alignment of Ravenna Creek (draining Green Lake southeast into Union Bay) and Carkeek Creek (northwest into Puget Sound), various stream drainages around Lake Forest Park (north end of Lake Washington), and (on the Eastside) the Northrup Valley (Hwy. 520 from Yarrow Bay to the Overlake area), and various smaller details too numerous to mention. All of these are carved into "recent" (less than 18,000 years old) glacial deposits, and it is difficult to conceive of how these could be controlled by anything other than a recent glacial process.

Yet the same orientation shows up in the Brothers, Euguene-Denio, and McLoughlin fault zones in Oregon (see map, below), which are geological features tens of millions of years old, and the Walker Lane lineament in Nevada.

Likewise to the east, where both the OWL and the Brothers Fault Zone become less distinct in Idaho where they hit the old North American continental craton and the track of Yellowstone hotspot. But some 50 miles to the north is the parallel Trans-Idaho Discontinuity, and further north, the Osburn fault (Lewis and Clark line) running roughly from Missoula to Spokane. And aeromagnetic and gravitational anomaly surveys suggest extension into the interior of the continent.

All of these alignments seem too strong to be random, but as yet it is quite a puzzle of how features millions of years old are linked with features only thousands of years young, and across hundreds of miles of diverse geology. Geology has not yet sorted this out. So this article will examine what the puzzle looks like before the pieces are assembled, touching on what may – or may not – be parts of the answers, and showing that shadowy zone at the edge of knowledge. Because geologists do not yet know even which pieces are relevant, a wide and even speculative view must be taken. This is what science looks like at the edge, before it is tamed and neatly trimmed.