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Portland, Oregon: A new geologic map detailing thick stacks of ancient lava flows, active earthquake faults and recent landslides on the western edge of the Grande Ronde Valley is being released on Monday, July 17th at the Governing Board Meeting of the Oregon Department of Geology and Mineral Industries (DOGAMI). The Governing Board Meeting begins at 8:30AM at the Oregon Department of Transportation Building, 3012 Island Avenue in La Grande.
Geologic Map of the Summerville Quadrangle, Union County, Oregon, DOGAMI Geologic Map Series GMS-111, encompasses one of the most spectacular and youthful rangefront fault systems in Northeast Oregon and includes the western edge of the Grande Ronde Valley and the dramatic escarpment that culminates in Mt. Emily with its commanding view of the valley. This fault zone may have been active in the past 10,000 years and may be capable of producing earthquakes up to a magnitude 7.
Mt. Emily is at the top of a large fault system, which has broken the stack of 13 to 17 million year old lava flows that make up the local bedrock. The movement of these faults has lifted the mountaintop over 6,000 feet. Well drillers encounter the same rock that caps Mt. Emily at a depth of over 2,000 feet beneath the valley floor. Several of the faults that have accomplished this tremendous uplift are still active, and may have moved during strong earthquakes in the last few thousand years. This fault zone is part of the larger (50 km or 80 mile long) West Grand Ronde Valley fault zone, which stretches from south of Union to north of La Grande.
Landslides along the face of Mt. Emily are another geologic hazard mapped in the quadrangle. Some of the landslides are large areas of slowly moving rock and debris, which may remain stable for long periods, and others, called debris avalanches, can move very quickly and spread destruction well out onto the valley floor.
The map includes information from water wells to help identify the important groundwater resources in the area. The mapping of the volcanic rock layers and faults also helps planners and water users understand groundwater resources, because these same lava layers hold the water tapped by deep irrigation water wells beneath the valley floor.
Crushed rock is the only mineral resource mined from the Summerville Quadrangle, but the new map shows that sand and gravel resources exists as well as low-temperature geothermal resources.
The Summerville Quadrangle was mapped by Mark Ferns and Ian Madin of the Oregon Department of Geology and Mineral Industries. The map is one of several geologic maps of Northeast Oregon being produced as part of the La Grande Mapping Project, which encompasses some 1,500 square miles. "This area has been targeted for detailed mapping by the US Geological Survey," explains Ferns. "The finished map will be useful in assessing the area’s earthquake risk, and water and mineral resources." Other completed maps include GMS-113, Geologic Map of the Fly Valley Quadrangle and GMS-110, Geologic Map of the Tucker Flat Quadrangle.
A comprehensive geologic map to be published in a few years will include the entire area from the west side of the Grande Ronde Valley through the Blue Mountains as far west as Ukiah and Pilot Rock. Mapping currently underway in the North and east of the Grande Ronde Valley will eventually be incorporated into a map of the entire Grande Ronde Basin upstream of Elgin.
Geologic of the Summerville Quadrangle, Union County, Oregon, , DOGAMI Geologic Map Series GMS-111, will sell for $10 and is available from the Nature of the Northwest Information Center, 800 NE Oregon Street #5, Portland, 97232, (503) 872-2750, www.naturenw.org; or DOGAMI field offices: 1831 First Street, Baker City, 97814, (541) 523-3133; and 5375 Monument Drive, Grants Pass, 97526, (541) 476-2496.
For more information on upcoming events and current projects, contact James Roddey at 800 NE Oregon St., Portland, OR 97232, (503) 731-4100, ext. 242 or DOGAMI field offices at 1831 First Street, Baker City, (541) 523-3133, 5375 Monument Drive, Grants Pass, (541) 476-2496, and the Mined Land Reclamation Program, 1536 Queen Avenue SE, Albany, (541) 967-2039.
The Oregon Department of Geology and Mineral Industries is headquartered in Portland and is an independent agency of the State. It has a broad responsibility in developing a geologic and engineering understanding of natural hazards, then applying this information to help mitigate the risks of earthquakes, landslides, floods, and tsunamis. The Department is also the lead state regulatory agency for mining, oil, natural gas and geothermal exploration.
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