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.

Tropical storms, which cross the Texas coastline with a frequency of 0.67 storms per year, play a major role in nearshore sedimentation on the south Texas coast. Greatest geological effects of these storms are produced by wind-driven waves and by storm surges.

The Blach Ranch and Breckenridge limestone members of the Thrifty formation are the most persistent mappable rock units in the Cisco group of the Brazos and Trinity River valleys.