Return to Ribbon Cliff Page
Taken from Daroga Park on the opposite bank of the Columbia River this picture shows Ribbon Cliff quite well. As described in the caption for the Earthquake Point photo, the light colored granodiorite contrasts strongly with the darker ribbons of basaltic dikes.
The landslide scar shows clearly as the lighter colored rock at the top of the cliff. If you imagine a rocky head similar is size to the one just at the right side of the photo, you can readily picture how much rock must have falled on that fateful December day in 1872. Even in such a short fall, only 1400 feet or so (!), that mass was thoroughly broken up and spilled into the Columbia as a landslide deposit. Most of the deposit is now drowned by Lake Entiat, Rocky Reach Dam's reservoir. However, some of it shows as the rounded foreground at the lower lefthand corner. On the site map noted on the Ribbon Cliff page, the mapmakers included the pre-reservoir contours of the site and you can see the bulge created by the toe of the slide.
At the base of the cliff are talus slopes composed of material that has fallen and been washed off the slopes before and since the earthquake. They are called colluvial fans as opposed to alluvial fans. Alluvium is deposited by running water whereas colluvium is formed by the action of gravity alone, from rock falls and similar processes. Notice, also, how the highway department has cut into these fans of debris. Although not visible in this photo, there are jersey-wall concrete barriers between the fans and the highway. And there are some pretty large rocks leaning against the cliff side of the barriers!Again, this is a morning photo. Although facing a bit more easterly than northeasterly, they cliff is well into shadow by early afternoon. This picture was taken at nearly the optimal time for the sun angle to accent the crevices and fractures in the rock face. The highway and railroad tracks follow the thin, dark horizontal line near the base of the cliff.
Photograph copyright © 1992-98 by Peter K. Matthews. All Rights Reserved.