THE ANCIENT LANDSCAPES OF SOUTH TEXAS, A GEOHERITAGE PROTOTYPE FOR THE LOWER RIO GRANDE VALLEY

The Lower Rio Grande Valley (LRGV) (population 1.3 million with an additional 150k seasonal residents), an area encompassing the 4 southernmost counties in Texas, is often associated with poverty, narcotrafficking and illegal border crossings. To fuel positive publicity, educate residents, and attract visitors to the LRGV, The Ancient Landscapes of South Texas, Hidden in Plain Sight trail, a Geoheritage initiative was formed. The trail highlights the rich and largely overlooked geologic and natural/cultural history of the LRGV, stretching along a 60 km wide corridor, from the mouth of the Rio Grande as it enters the Gulf of Mexico, to the city of Roma at the western end of the LRGV, a distance of 240 km. The trail incorporates the geologic events that shaped south Texas over the last ~43 million years, as seen at easily accessible outcrops including, the old shoreline of the Gulf of Mexico, (The Roma Sandstone) the associated giant oyster reefs; a 20 m think volcanic ash deposit (the Catahoula volcanic ash), and evidence for a petrified forest. Equally important are sites or objects of natural interest and beauty including, the oldest object in south Texas, the 20 pound La Villa Meteorite, the oldest living organism in the LRGV, the 900-year-old Montezuma cypress, or the unique wind-tidal flats with the resilient algal mats. Also prominent on the trail are the geologic resources available to the first humans who arrived in the area, among those are the salt flats exploited since prehistoric times, and the distinctive El Sauz Chert used to make spear and projectile points for ~10000 years. A section on the Paleobiology of the area features big Pleistocene game that lived on the continental shelve when sea level was lower, and a thriving community of giant tortoises. Lastly, the trail includes visits to a series of water wells, hand dug in the 1850’s through ~10-meter-thick layer of resistant caliche. These wells made cattle ranching possible in an otherwise uninhabitable environment. While some of these sites have been well known natural attractions for years, the majority are unknown to even local residents.