Projected profiles drawn from published topographic maps across the outcrop of the Trinity Group show the basal erosion surface to be preserved only a few miles updip from the outcrop. The surface, projected upward toward the Oklahoma mountains, passes well above the present tops of the mountains. Changes in the rate of slope along the strike indicate that it has been affected by late or post-Comanchean pre-Woodbine movements. Later movements have brought it to its present attitude. The present rate of slope ranges from about 30 ft/mi to 130 ft/mi or more, the maximum rate being reached near the core of the Ouachita Mountains.

Similar profiles for the Woodbine show the basal Woodbine surface to be preserved an even shorter distance updip from the outcrop. This is probably due to the less resistant nature of the pre-Woodbine beds compared with the pre-Trinity beds. The present rate of slope of the pre-Woodbine surface ranges from as little as 20 ft/mi to as much as 80 ft/mi or more. The maximum rate is reached near the core of the Ouachita Mountains.

A comparison of the rates of slope of the two surfaces shows the pre-Woodbine surface to be in general a subdued replica of the pre-Trinity surface. The difference in the slope rates of the surfaces indicates that vertical uplift of more than 1,200 ft occurred in the Arkansas part of the core of the Ouachita Mountains during that interval of time. Corresponding subsurface data in south-central Arkansas indicate that a greater amount of uplift occurred there--possibly on the order of 5,600 ft at the Ouachita axis.