Clastic Dike at Craig's Hill, Ellensburg WA


Cryptic reports of this feature have floated around for decades, so I figured its time I document it. The dike is located in the bluff right above the holding pens at the Ellensburg Rodeo grounds, below the water tower. Its white. You can't miss it. Every CWU Geology student has seen surely seen it. The American Legion's Vista House is seen at upper right of photo.

The Craig's Hill clastic dike cuts fluvial, overbank, and hillslope deposits with paleosols (Ellensburg Fm). Stratigraphically, there's quite a bit going on in the fine-grained strata that overlie the more conspicuous gravels exposed at road level. Pencil for scale.

There's actually two dikes at Craig's Hill. This is the smaller one. Though not quite a "Touchet-type" clastic dike (it lacks sheeting), some similarities exist. Its color and composition are interesting. The fracturing in the larger dike is too. I found no other dikes in the hundreds of meters of Ellensburg Fm exposed at Craig's Hill, but maybe you have. If so, please let me know.

A portion of J.J. Mabry's figure from her Field Trip Guidebook to the Natural History of Kitittas County (Mabry, 2000, p. 24). The author credits an unpublished figure by M. Williams of Central Washington University (c. 1991). Stratigraphic interp is creative.

This guy is standing just uphill of the outcrop. The photo was taken a long time ago, back when Ellensburg Rodeo spectators watched cavemen riding dinosaurs.

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