GEOLOGY OF THE WAR EAGLE QUADRANGLE, BENTON COUNTY, NORTHWEST ARKANSAS

The War Eagle quadrangle is located on the Salem and Springfield Plateau surfaces, on the southern edge of the Ozark Dome in northwest Arkansas. Approximately 12 square miles of Beaver Lake are located in the northern portion of the quadrangle. Around 15 square miles of Hobbs State Park – Conservation Area are located in the south half of the quadrangle. Recent mapping highlights a refined stratigraphic sequence, normal faults, and karst features.

Approximately 500 feet (152 meters) of Lower Ordovician to Upper Mississippian strata crop out in this area. Lower Ordovician strata forming the Salem Plateau are present in the northern portion of the quadrangle. The Lower Ordovician Cotter Dolomite is present only on the north-central part of the quadrangle where it is upthrown by the Fayetteville Fault. The Lower Ordovician Powell is also thicker in this area. The Devonian Chattanooga Shale and Clifty Formation are thickest on the downthrown side of the Fayetteville Fault in the east-central part of the quadrangle. The lowest sandstone bed(s) included in the Clifty could be Ordovician in age. The Lower Mississippian Boone Formation covers most of the quadrangle forming the Springfield Plateau. The St. Joe Limestone, at the base of the Boone, is a small bluff former throughout the area. The Chesterian Batesville Sandstone crops out in only two locations: downthrown by the Fayetteville Fault in the southwestern portion of the quadrangle and south of the Devils Gap Fault along the southeastern border of the quadrangle.

Two major normal faults are located on the quadrangle. The Fayetteville Fault strikes southwest to northeast across the quadrangle and is downthrown on the southeast side, while the Blackburn Creek Fault (Dowell, 2004) strikes east to west across the quadrangle and is downthrown on the north side. The trend of the Blackburn Creek Fault continues across the Fayetteville Fault, however, in the eastern half of the quadrangle, it is downthrown on the south side. Displacement along the Fayetteville Fault varies from 60-100 feet (18-30 meters) and offset along the Blackburn Creek Fault is approximately 60 feet (18 meters). The Devils Gap Fault to monocline is a normal fault downthrown on the north side with displacement of approximately 40 feet (12 meters).

Karst features include springs, caves, and sinkholes which are most abundant in the St. Joe Limestone. Karst also includes spectacular sandstone paleokarst masses in the Powell Dolomite.