Portland State University. Department of Geography
Date of Award
Master of Science (MS)
1 online resource (147 p.)
Geology -- Oregon, Structural Geology
Stone stripes are linear accumulations of rock debris separated by finer material and oriented down the steepest available slope. In north central Oregon, the stone stripes are composed of basalt fragments and occur where the soil mantle averages less than 1 m in depth. They are best developed in areas of higher elevation, usually from about 900 to 1100 m, and are most prominent on convex to straight slopes of 15 to 30 degrees. The stripes vary from a few meters to over 150 in length, and their widths range from 0.3 to over 3 m. The depth of the stone stripes ranges from 20 to over 65 cm. Morphological investigations of stone stripes in north central Oregon reveal that: (1) surface rock orientation is not very strongly related to slope direction or gradient; (2) stripe depth does not seem to be connected to width of the stripe nor to position on the slope; (3) vertical sorting occurs in a rock size ratio of about 5:3:2 from surface, to middle, to base; (4) the introduction of cattle has resulted in considerable stripe modification; and (5) vegetation encroachment and infilling with soil are stabilizing the stripes from the edges inward.
The stone stripes found throughout north central Oregon are of such a size and magnitude that they cannot be adequately explained by geomorphic processes currently operating in the region. Although these processes are sufficient to cause some stripe movement and modification, the initial striped patterns were probably developed under periglacial conditions during the cooler, moister phases of the Quaternary. Evidence which lends credence to a cold climate origin for these stone stripes includes: (1) other forms of patterned ground, i.e." sorted circles, nets, and polygons; (2) soil mounds; (3) talus slopes; (4) terracettes; (5) convex slopes; and (6) stripe stabilization through vegetation encroachment, soil infilling, and heavy lichen growth.
Pyrch, John Baine, "The Characteristics and Genesis of Stone Stripes in North Central Oregon" (1973). Dissertations and Theses. Paper 1610.