Saturday, November 5, 2016

Wenatchee Formation and Randy Gresens

Wenatchee Formation above Squilchuck Creek

Once upon a time I was pretty familiar with the Wenatchee Formation as well as the Swauk and Chumstick. These rocks are within a structure called the Chiwaukum Graben, a fault bound, dropped downed block. The formations within the graben structure were formerly more wide-spread, but were subsequently eroded as the Cascade Range uplifted; the old graben structure has preserved a section of these formerly more wide spread rocks that may have correlative formations on the west side of the Cascade Range.

My understanding of these rocks had gotten a bit rusty. It had been so long that I had forgotten that I once did some geologic excursions up the Squilchuck Creek valley south of Wenatchee. My memory of that time got a boost when I saw the slope pictured above. I visited this slope with Randy Gresens, a professor of mine, during my in and out of school era. I had just returned to college for the third time when I went on this trip. We took two field trips and one was up the Squilchuck drainage. This slope provided a good introduction to the Wenatchee Formation.

Randy Gresens mapped this area and two quadrangles to the north.

The maps are highly detailed and the report with the maps provides detailed and very specific site location descriptions. It is a model of how a good quadrangle map should be done. In retrospect, I realized that those field trips were to places that were just beginning to be understood by the mapper. The way I recall the second trip, we did not find what we (Dr. Gresens) were hoping to see - that is I got to experience a theory being tested and that theory being proved wrong, a good lesson for a student.

The map publication took place after Dr. Gresens died in a plane crash. The crash took place above the Squilchuck drainage in the Mission Ridge area. Eric Cheney, another professor, wrote a memorial for his associate: I did not know Dr. Gresens beyond the two classes I took from him, but he treated me fairly in one class I was ill prepared for (geochemistry) and he expanded my field background with those two trips to the rocks in the Chiwaukum Graben.

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