Northwest Energy Association

NWEA Speaker Program for 2019-2020

Thursday,  November 21, 2019

11:30 am - 1:30 pm, Multnomah Athletic club

When did the Cascade Range in Washington rise?

Eric S. Cheney, ESS, University of Washington, WA 98195;

The consensus that the topography of the Cascade Range in Washington is 30 to 40 Ma is wrong.  Because flora in the 17 to 15 Ma Columbia River Basalt Group (CRBG) and overlying < 9 Ma Ringold Formation on the eastern side of the range do not record a rain shadow, no significant mountain range existed by then).   

The SSW striking Cascade Range anticlinorium (CRA) is clearly outlined on the east by easterly dipping CRBG.  On the mostly covered western limb, < 12 Ma formations define the SSW striking Puget synclinorium.  Thus, the CRA is < 12 Ma.

The 4 Ma Thorp Gravel and Simcoe Mountains basaltic rocks (SMB) on the eastern limb of the CRA dip 3⁰- 5⁰ E.  The SMB overlies a correlative of the < 9 Ma clastic Ringold Formation.  Because calcretes are ubiquitous atop the youngest member of the Ringold Formation in the Hanford area, the rain shadow and uplift of the range are < 4 Ma.  

 A trend surface on 205 peaks in the southern Cascades that are underlain by > 5 Ma rocks is antiformal, doubly plunging, SSW striking , and has a relief of 1.4 km.  The 1.3 Ma Tieton andesitic valley flows are incised into the eastern limb of the CRA. Thus, the CRA mostly formed between 4 and 1.3 Ma.  The more popular name of the CRA, the Cascade magmatic arc, obscures its identity and age.

Short Biography of Eric S. Cheney

Eric Cheney received his BS and PhD from Yale University.  He has been at the University of Washington since 1964 (the Middle Proterozoic); he semi-retired in 2005.  He was a visiting professor at Stanford University and two universities in South Africa. At UW his teaching and research included the geology and social relevance of mineral and fuel deposits and the geology of the Pacific Northwest.  
 In Washington, his geologic field mapping and that of his students has elucidated the geology ore deposits, the Skagit nuclear power plants in the 1970s, metamorphic core complexes, the stratigraphy and structure of pre-Jurassic North America, the Quesnel terrane, and inter-regional Cenozoic stratigraphy and structure.  The main tool in these and other contributions to the geology of southern Africa and Western Australia has been unconformity-bounded stratigraphic sequences. What has been lacking until now is any serious foray into Pleistocene geology.
 In 1987 he was cofounder and the first President of the Northwest Geological Society in its present reincarnation.  He has led many field trips and been a frequent speaker at NWGS. He is also a member of the Society of Economic Geologists, the Geological Society of America, the Society of Mining Engineers, and the American Exploration and Mining Association.

Future NWEA Meetings 2019-2020

Thursday January 16, 2020

Thursday February 30, 2020

Thursday March 19, 2020

Thursday April 16, 2020

Thursday May 21, 2020