- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
The tectonically active trough containing the Colorado River delta appears to be a northward extension of the Gulf of California. Sedimentary rocks in the trough divide into, (1) Miocene, Pliocene and Pleistocene fanglomerates, conglomerates, breccia, and coarse arkosic sandstone, and (2) Pliocene and Pleistocene clay, silt, and fine sandstone. Coarse sediment was derived locally; fine sediment was transported by the Colorado River, and derived mostly from the Colorado Plateau. Cretaceous Mancos Shale foraminifera are found in the Pleistocene delta sediments.