43 MYA Gulf of Mexico Shoreline
DEPOSITED 43 MILLION YEARS AGO WHEN THE SHORELINE OF THE GULF OF MEXICO WAS NEAR ROMA ARE THE OLDEST EXPOSED ROCKS IN THE LOWER RIO GRANDE VALLEY.
On the western side of the Rio Grande Valley in Roma, we find evidence of a sandy shoreline much like South Padre Island is today. The Roma Sandstone is evidence of its existence. Over the past 43MY, the coastline has prograde over 100miles east to its current position.
The “Roma Sandstone” is a local informal name for a portion of the Eocene-age Jackson Formation exposed in the cliffs below Water Street in Roma, Texas, and isolated outcrops elsewhere in that region. At the Roma Bluffs, the massively bedded and very resistant sandstone is underlain by thinly bedded layers. These layers are eroding faster in a cut bank of the Rio Grande that runs at the base of the bluffs resulting in undercutting and periodic collapse of large blocks down the nearly vertical cliff face. The bluffs are a World Birding Center site and provide a unique view of a portion of the Mexican border town of Ciudad Miguel Aleman and the international bridge.