The Many Stories of the Wallowa Mountains

December 08, 2014


Photographer: Marli Miller  
Summary Author: Marli Miller

December 2014 Viewer's ChoiceThis photo of the Wallowa Mountains shows an accreted terrane, a stitching pluton and flood basalt all in one view. Sawtooth Peak, on the right, consists mostly of Mesozoic granite of the Wallowa Pluton but is capped by the reddish Columbia River Basalt. The pluton intrudes the bedded rock on the left, which belongs to the Triassic-age Martin Bridge Limestone (see interpreted photo below).Wallowadetail

These rocks tell an amazing story. The Martin Bridge limestone likely originated as a coral reef complex in the far Western Pacific Ocean but accreted to the edge of North America during the Jurassic period as part of the Wallowa Terrane. Intrusion of the granite occurred in stages between 140 and 122 million years ago and places an upper limit on when this accretion occurred. It’s called a stitching pluton because the intrusions appear to stitch the terrane to the edge of the continent after accretion. After a period of uplift and erosion, the Columbia River basalt covered this region between 17-14 million years ago. Eventually, more uplift of the Wallowa Mountains occurred elevating the basalt to 9,838 ft (2,999 m). Photo taken in Joseph, Oregon.

Photo Details: Camera: Canon EOS 5D Mark II; Lens: EF100-400mm f/4.5-5.6L IS USM; Focal Length: 400mm; Aperture: f/10.0; Exposure Time: 0.0063 s (1/160); ISO equiv: 50; Software: Adobe Photoshop CS6 (Macintosh).