Paleosol: A brilliant red clay layer up to 60 feet thick lies on top of the D1 Synorogenic Strata. This red clay formed as ancient soil, similar to modern red soils that have formed in the moist climates of the southeastern United States and the Amazon Basin of Brazil. The presence of the layer suggests that it was exposed and weathered for a very long period of time, perhaps as long as 9 million years. The clay is mined to make bricks.