Eagle Mountains and vicinity include three physiographically distinct but stratigraphically and structurally related sub-units: a central, topographically high mesa, Eagle Mountains; a much lower northwestward extension, Devil Ridge; and a south-southeastward extension, Indio Mountains. These highlands, trending generally northwest to north-northwest, are surrounded by "bolsons" or inter- montane basins partly filled with alluvium.

The Red River rises in northeastern New Mexico and extends across northern Texas and east of the Panhandle serves as the northern border of that State. The late Cenozoic geology of the Red River basin has been studied intensively in northwestern Texas and in Louisiana. This report summarizes the results of our studies of the late Cenozoic geology of the Red River basin in Texas. Late Tertiary terrace deposits have been identified as far east as Montague County and deposits of Nebraskan age have been recognized somewhat farther east.