Contacts Bureau of Land Management
Vale District Office
100 Oregon Street
Vale, OR 97918

The geological background of this province is based in volcanic activity which started in the Miocene. There are deep volcanic deposits of basalts, tuffs and tuffaceous sediments. While basalt is prevalent, other features include rhyolite, diatomaceous deposits, new sedimentary deposits and new surface lava. The episodes of deposition affecting the Owyhee uplands include the Owyhee Basalts that erupted onto the plateau 13-12 million years ago and the ash-flow tufts from the Steens mountains around the same time. In a few areas there has been relatively recent volcanism, of special note is Jordan Craters.
The Jordan Craters lava flow is located in the Owyhee uplands on the plateau. It is a 75 square kilometer olivine basalt flow that is extremely recent by geological time. Potassium argon (K-Ar) dating shows that it is no older than 30,000 years. However, "studies based on growth rates of lichen and weathering rates of exposed and unexposed basalt suggest that the flow may be between 4,000 and 9,000 years old". "Additionally the southeasterly flowing lava altered ancestral drainage patterns, giving rise to a natural dam and the formation of two small lakes (Upper and Lower Cow Lakes)"

For more info See Malheur County Website at: www.malheurco.org

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