Clastic Dike at Craig's Hill - Ellensburg, WA
Craig's Hill is located in Ellensburg, WA at the Rodeo Grounds near the Campus U-Tote-Em burger joint. Easy walkable access via roads along the base of the exposure.
Cryptic reports of this clastic dike have floated around for decades, so I figured I'd document it. The dike is located in the bluff right above the holding pens at the Ellensburg Rodeo Grounds, below the water tower. It is white so you can't miss it. Every CWU Geology student has seen surely seen it. The red-roofed American Legion's Vista House is seen at upper right of photo and in the Google Earth map above.
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 tuffaceous fine-grained sediments 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 sheeted like a "Touchet-type" clastic dike, it does appear to descend. See its sloping margins that crosscut gray, sandy sediment? A funnel-like shape. Its white color and composition are also interesting, as is the fracturing in the larger dike that contrasts withthe surrounding sediment. What's the white material? I found no other dikes 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 The author credits an unpublished figure by M. Williams of Central Washington University (c. 1991).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.