Recently completed geologic mapping locates major faults and folds and shows the distribution of major stratigraphic units in the frontal Ouachita Mountains of Arkansas. The units constitute a thick Carboniferous flysch sequence with gradational depositional contacts. Stratigraphic units previously named in Oklahoma are applicable to the map area with the exception of subdivisions of the Jackfork Group (Irons Fork Mountain and Brushy Knob Formations).

Three major high-angle, east-west-trending thrust faults cross the area and probably flatten out to become bedding-plane thrusts. At one folded fault plane, the upper plate apparently has been eroded away, exposing the lower plate for almost 30 mi along the upwarp. Folded thrust planes have not been described previously in the frontal Ouachitas of Arkansas and the exposed window in the map area comprises the largest such structure anywhere in the Ouachita Mountains. The impetus for thrusting and folding probably was uplift of some large area in the south, causing northward sliding and eventual folding and faulting of the water-charged sedimentary succession. This uplifted area subsequently was truncated and overlapped by Mesozoic and younger rocks.