Sediments in the Ouachita Mountains area have been changed by heat and pressure, but not too much. Some areas show no change, while others have been altered more. The type of rock and how broken it is help us see how much the sediments have changed. Sandstones become less porous and can't hold oil well after metamorphism. Rocks in Luling, Texas, are similar to those in Oklahoma, showing the same changes from metamorphism.