Changes in the position and stability of shorelines in the San Antonio Bay system (San Antonio, Espiritu Santo, and Mesquite Bays), Texas Gulf Coast, were documented using historical monitoring techniques.

These cross sections numerically correspond to previously published onshore cross sections (CS0002--Dodge and Posey, 1981) and extend those sections across the continental shelf into the Miocene, a recent target of renewed petroleum exploration.

The publication comprises 24 structural dip cross sections, spaced 15 to 20 mi apart along the Texas coast, and 4 structural strike cross sections. Dip sections extend from near the Wilcox outcrop to the coastline.

Upper Miocene, Pliocene, and Pleistocene deposits in the subsurface of the central Coastal Plain of Texas were subdivided into six operational units comprising the surface-defined Fleming, Goliad, Willis, Lissie, and Beaumont Formations.

Secondary leached porosity is common to dominant in near surface to deep subsurface lower Tertiary sandstone reservoirs along the Texas Gulf Coast. This secondary porosity is in the form of leached feldspar grains, volcanic rock fragments, carbonate cements, and carbonate-replaced grains.

The State-owned submerged lands of Texas encompass nearly 6,000 square miles (15,540 km²) and extend from Mexico to Louisiana. The area includes the bays, estuaries, and lagoons, as well as the inner continental shelf 10.3 miles (16.6 km) seaward of the Gulf shoreline (fig. 1).

Approximately 800 sediment samples from stream beds and bay bottoms of water bodies that compose the Matagorda Bay system were collected and analyzed. Shell-sand-mud ratios and total organic carbon content were determined, and 20 trace elements were detected.

Sequential shoreline monitoring, using vintage chans and aerial photographs, documents temporal and spatial variations in historical Gulf shoreline changes.

Historical monitoring along Matagorda Island and San Jose Island records the nature and magnitude of changes in position of the shoreline and vegetation line and provides insight into the factors affecting those changes.