Tuesday, April 26, 2011

A Few Notes on the Interstate-82 Landscape

I just got back from a trip to eastern Washington. Much of our view of the landscape is via what we see while zipping along interstate freeways. While slowing down to take back roads and making stops may lead to a better understanding of the land, frequently distance and the need to get somewhere in a short time precludes further exploration. So a few notes on a few drive by features along the I-82 route from Kennewick to Ellensburg.
Landslide east of Prosser.

Upon entering the Yakima Valley the freeway traverses the base of the steep front of the Horse Heaven Hills between Benton City and Prosser. The ridge line is a very asymmetric anticline and the fold is so tight along the ridge line that the rock basalt and relatively thin sediments between the basalt flows is highly fractured and may be slightly faulted as well. As such there are a large number of big landslides that give the slope a lumpy appearance. I always thought that these slopes would make a great ski area if only the climate was not so dry. The slides are very old features. Some of the slides appear related to the fact that the lower half of these slopes were inundated by the Missoula floods when water backed up at Wallula Gap. Most of the land on the steep slope is managed by the Bureau of Land Management with one section of Washington State Department of Natural Resources managed land. Cattle grazing has been allowed in the past, but if it currently is allowed it is at a much reduced level than in the past.

Rythmite silt deposits near Zillah

Near Zillah is a fantastic exposure of Missoula floods silt deposits. Each layer of silt was deposited by a flood event where the water was backed up the Yakima Valley during the numerous Missoula flood events. This is the best freeway view. These beds are often referred to as Touchet Beds as equivalent layers are preserved in the Walla Wall Valley near Touchet. The steep slope is a cut bank from the Yakima River which is located on the opposite side of the freeway. I always enjoy seeing this exposure.


I previously did a post on Pushtay HERE. I have often been asked about this out of place conical hill. The rest stop north of Selah is a worthwhile spot to take a break. A short walk to the fence line provides a nice view of Pushtay as well as the deeply incised Selah Creek canyon. This view is from the north bound rest stop, but the south bound stop is a great stop as well with overview of the Selah Cliffs Natural Area - Department of Natural Resources protected area with numerous rare plants.

Freeway bridge spanning Sehah Creek gorge

Interstate 82 leads to Interstate 90 near Ellensburg. Near Cle Elum, Will and I could see that the rain shadow had been in full effect and that we would be returning to cloudy rainy weather.

Clouds breaking apart while passing over the Cascade Range


Scott Schuldt said...

Last May, I canoed the Yakima River from Ellensburg to the Columbia River. It was fascinating to watch the land change as we progressed. The river near Zillah was braided with round river rocks. A sedimentary cliff formed the north side of the river as we neared Granger. Then it was big meanders in a treeless scrub, the river down in a deep mud bank most of the way to Prosser. It was after the portage through Prosser that the river really changed. The river bottom there was large boulders. Sometimes the river had an amazingly steep angle to it, but the current was only moderately fast, I figure do to the toothiness of the bottom.

Dan McShane said...

Scott: that sounds like a great trip. As this last drive was a freeway view of the landscape I did not have any good shots of the river area as my attention was on the green slopes above the freeway downstream of Proser. The rocky nature of the river downstream of Proser is the result of the rapid draining of the short lived lake during the Missoula Floods. The current stripped away the silts here and there are significant areas of scabland topography just above Benton City.