Mildly deformed sedimentary rocks of the Northern Rocky Mountain Trench were analyzed for their spore and pollen content. From these it was deduced that the rocks were of Early Oligocene (Chadronian) age. Two conclusions were reached: (1) at least mild deformation occurred in this portion of the Trench following the Early Oligocene and (2) Early Oligocene climate appears to have been essentially subtropical of a summer-wet, winter-dry type. These add further evidence to the theory that the Rocky Mountains were already of considerable elevation by Early Oligocene time.

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