Comparison of the above terranes map with the geologic units map for all of western Oregon (below) of much of the same region demonstrates a close correspondence

between some units and their enclosing terranes, a broader correspondence for others, a number of individual units that are scattered about within the terranes, and some units that seem to cross over or overlap terrain boundaries. (Because there are so many units [generally, at the formation level], the map's legend is not shown; also, in the legend sequence are units not present in the Klamaths.) Two examples of exceptions are the deep purple unit (Jui), which is actually outliers of ultramafic (ophiolitic) lavas once part of oceanic crust which appear similar in the field but originated locally within their terranes, and the pinkish-red unit, which consists of intrusive rocks that invaded several already in place terranes. This general agreement between terranes and their constituent stratigraphic units (i.e., internal consistency) is to be expected, along with the exclusivity of some units to single terranes, inasmuch as terranes typically develop from rocks formed in different source areas at different times.

The Oregon Klamaths are among the most rugged landforms units in the state. A sense of their appearance is gained from inspection of this 3-D perspective image of nearly all of Oregon, generated from DEM data:

Features of interest in this shaded map are: A = Klamath Mts.; B = Coast Ranges; C = Willamette Valley (Portland at north end); D = High Cascades; E = Mt Hood; F = Crater Lake; G = Paulina Mts (Newberry Crater); H = Blue Mts.; I = Abert Rim; J = Summer Lake area (the circularity is somewhat an artifact of the illumination)

A feel for the appearance from the ground of several of the Klamath terranes is gained through these photographs taken during the writer's time in the field:

The upper left scene shows terrain around Canyonville, with Yolla Bolly terrane in the foreground and Sixes River terrane in the distance. Next to it is a view from the coast of the Elk terrane. In left center is a segment of a canyon dissected by the Rogue River in which sedimentary units of the Rogue Valley terrane (Jrv) are exposed. To its right is landscape typical of the higher elevations in the Klamath Mountains. The lower left scene is an exposure of serpentinite (the metamorphosed ophiolitic basalts associated with oceanic crust). The lower right shows alternating layers of siliceous (cherty) shales that constitute island arc sediments; here they are part of the Yolla Bolly terrane.

A preview of the topographic expression of the Klamath Mts, which we will present from Landsat shortly, is afforded by this enlargement of the area made from the same DEM data; notice Crater Lake (nearly circular on top of a mountain) in the upper right part.

In this visual version, it is difficult to spot by eye any significant variations in terrain that call attention to noticeable terrane differences. Of course, directions of illumination can be varied to emphasize contrasted ridge and valley orientations; this was done on this data set giving several distinct expressions but, again, obvious patterns that correlate with the various terranes as mapped did not stand forth, although when one learns where to look, after familiarization with terrane locations, strong hints of certain differences for several of the terranes are discernible. These differences may also be disclosed by appropriate analysis of topographic data in map sheet or DEM formats and, in fact, this approach proved to be superior to visual differentiation.

The reason one would postulate for expected differences is this: each terrane consists of an assemblage of rock types that likely will differ to varying extents from other nearby terranes. Each is also bounded as least partly by fault discontinuities. A terrane will respond to regional erosive action according to its mix of lithologies. Thus, any one terrane may well develop landform characteristics that differ from its neighbors and can appear visually as separable. One should be cautious about expecting the differences to be confined neatly within terrane boundaries because, as the landscape develops within any one terrane, the equilibrium forms tend to exert some influence on terrains outside the boundary. Nevertheless, the hope in testing the hypothesis of distinctive terrane-controlled topographic expression is that real differences do occur.

In planning the geomorphic analysis, this strategy was set forth:

This effort is predicated on making a series of quantitative measurements that could be subjected to numerical and statistical tests to ascertain valid differences in the topographic character of each terrane. In general, none of these measures can be extracted with confidence from Landsat imagery; however, one SPOT image pair was available, so that stereo could be achieved, allowing limited recovery of measurable variables. So, in the exposition that follows, Landsat's prime role is to help to confirm the terrane-terrain association by visual recognition.

---

[an error occurred while processing this directive] [an error occurred while processing this directive]