The Saddle Mountains form a coherent ridge that runs for more than 80km east to west across south-central Washington. The ridge is a north-vergent uplift with thrust faults on its northern flank. There is a prominent footwall bench along a portion of its north flank called Smyrna Bench, which is composed of sediments younger than the basalt bedrock (Pliocene Ringold Fm, Pleistocene flood deposits, and calcretes). Strata on the south flank of the range rolls gently into the broad syncline of Pasco Basin. Cross sections through the Yakima Fold Belt in south-central Washington (top) and the Saddle Mountains anticline near Sentinel Gap (bottom). Thrust geometries are a bit old fashioned, but you
An exotic clast-bearing conglomerate at White Bluffs Overlook was left by an ancient Ice Age flood. The post-Ringold unconformity appears to be a sequence-bounding surface that may correlate with a late-Neogene unconformity in the Rocky Mountains. Flat-lying Pliocene Ringold lake beds (<5 Ma) are unconformably overlain by a meter-thick conglomerate composed of subangular calcrete rip-ups mixed with exotic clasts (granite, schist, andesite, quartzite). The conglomerate is Pleistocene age, likely a bit younger than 1.5 Ma. Exotic clasts derive from outside the Columbia Basin; they were brought here from the north and east by a combination of ancient rivers (ancestral Columbia, Salmon-Clearwate
Calcretes are hard pan soils that form in semi-arid to arid climates. Calcretes - at least pedogenic CaCO3 cements - first appear in Pliocene Ringold strata at Saddle Mountains between 7 and 5 million years ago. Arrival may coincide with onset of dry climate created when the Cascade Range achieved sufficient elevation to block wet Pacific weather systems from moving inland. Eastern Washington was quite a wet place until the orographic barried formed. While convergence at the plate margin and rock uplift in the Cascades began tens of millions of years ago, it seems the Cascades achieved their storm-blocking height quite late. In short, there appears to be a disparity between rock uplift over
The kame terraces of the Okanogan Valley are Alaskan in scale, but treeless and fully exposed. This extensive multi-level flight is continuously exposed between Brewster and Osoyoos, a distance of 100 km. The terraces record voluminous ice-marginal sedimentation during the final downwasting of the Cordilleran Ice Sheet (Okanogan Lobe) from Eastern Washington. They are composed of a mix of outwash gravels, till, lacustrine sediments, and boulders. Tread surfaces are paired in places, unpaired in others. Surface connections between terrace systems in the Methow, Sanpoil, and Upper Columbia are certain to be made. Fields of kettles dot many surfaces as do large erratics (mostly basalt, granite)
J Harland Bretz introduced the world to the vast and deeply scoured Channeled Scabland. Baker calculated flood volumes and the velocity of the flows. Waitt deciphered flood count and timing. The sedimentary record is known by the work of numerous authors and dozens of localities. Deformation caused by the cataclysmic Ice Age floods remains a frontier. In my new book, Flood Injectites of the Columbia Basin, I describe a suite of flood-caused deformation features along a 500 km transect from Priest Lake, ID to the Dalles, OR. Deformation varies with changing substrate characteristics and location within the floodway. The same floods triggered the formation of clastic dikes in certain places an
In 1941, the talented cartographer Erwin Raisz of Harvard University's Institute of Geographical Exploration published a map showing the Olympic-Wallowa Lineament, a "straight four-hundred-mile-long structural line extending from Cape Flattery to the Wallowa Mountains". The Olympic-Wallowa Lineament crosscuts the whole of Washington, extending from Cape Flattery to the Wallowa Mountains in Oregon. Map by Reidel and Martin (2003). The prominent line diagonally bisects Washington State and was immediately suspected to be deep crustal structure expressed at the surface as a series of aligned basins and faults. That is, the sum of all fears: a huge, long-lived fault zone running through major po
Geologists have long debated how large of an earthquake faults in the Yakima Fold Belt are capable of producing. Some claim these shallow (<10km), intraplate structures are capable of generating quakes up to 7.0 magnitude. Others estimate their capability no higher than about 6.0 magnitude. The difference between 6.0 and 7.0 is huge. I've personally experienced two quakes larger than 7.0 M. Believe me, crazy sh*t happens above magnitude 7. I've also been in several 6.0 M quakes. Those, by contrast, were little more than brief amusements. I throw my lot in with the lower-estimate camp, based on my experience working in the unconsolidated sediments of the greater Columbia Basin for more than 2
