Geology and History of San Antonio

Geology of San Antonio

The City of San Antonio’s story begins between 65 and 145 million years ago when a vast inland sea covered the western interior of what is now North America. During this time, marine sequences consisting of limestones and clays were deposited. As the Cretaceous Period drew to a close, the extensive continental sea began to retreat toward the Gulf Basin. During this time, South Central Texas was receiving sediments from the eroding Rocky Mountains and thousands of feet of sediment accumulated. During the Miocene, the weight of these sediments created tension and caused faulting to occur. The Balcones Fault Zone was created as a result of this tension, leaving San Antonio on a “hinge” between the flat lying Edwards Plateau and the gently sloping Gulf Coastal Plain.

History of San Antonio

The area we now know as San Antonio was called "Yanaguana" (Land of Spirit Waters) by the Native Americans who lived there for millennia. Spanish explorers first visited the area in 1691 and established the Mission San Antonio de Valero (later called the Alamo) in 1718. Spanish settlers were drawn to the area by the abundance of fresh water springs. They built Catholic missions and an extensive system of irrigation ditches called acequias. These acequias diverted water from the San Antonio River to the missions and accompanying fields. San Antonio grew to be the second largest Spanish settlement in Texas. In 1836, Texas won its independence from Mexico—just a few months after the battle of the Alamo—and was annexed into the United States in 1845. All this time, the city of San Antonio continued to thrive and has grown into the city we see today.

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