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 structure called the Chiwaukum Graben, a fault bound, dropped downed bock. 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. http://file.dnr.wa.gov/publications/ger_b75_geol_wenatchee_monitor.pdf.
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 above the Squilchuck drainage in the Mission Ridge area. Eric Cheney, another professor, wrote a memorial for his associate: geosociety.org/pub/Memorials/v14/Gresens-RL.pdf. 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.