Geological Tables
Table Rocks, Oregon

compiled by the Editor

The American Table Rocks are found in the Rogue River Valley of southern Oregon. They comprise two horseshoe-shaped 'tables' and a number of minor monolths standing 250 m above the valley floor. The flat summits of these tables are formed from alkaline trachyandesite and are remnants of a much more significant lava flow that once filled the valley.

During the early Palaeogene, the Rogue Valley was submerged and accumulated a sequence of marine and littoral silts and sands. During the mid to late Palaeogene, tectonic uplift brought the Rogue Valley and Younger Cascade Mountain Ranges to their current position. As uplift continued through the late Palaeogene and early Neogene, a number of canyon features were developed, the ancestral Rogue River Canyon being one of these.

Late Miocene shield volcanic activity in the Cascade Mountains to the east formed a number of features such as Crater Lake, now a National Park, and the Devil's Peak, not to be confused with Devil's Tower, Wyoming, where Close Encounters of the Third Kind was filmed. Around 7.5 million years ago, alkaline trachyandesite lava was erupted from a vent near Lost Creek Reservoir. This spread as a sheet flow over the area and, finding the Rogue River Canyon, chose this as a natural conduit, filling the valley.

During the Pliocene and Pleistocene, the Rogue River once again asserted its claim and began, slowly at first, to erode down through the lava flow. Meltwaters from the Cascades increased the effect of the river in eroding the rock and now only a few remnants are left, 90% of the lava having been removed by erosion. Two of these remants are known as the Table Rocks of South Oregon.

Figure

Late Miocene lavas forming the table top on Lower Table Rock, Oregon
 
 
 

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