2 History 



Local Geology 



Geologic development in the area of the mouth of the Colorado River 

 consisted of alternating deposition and erosion related to the advancement and 

 retreat of continental glaciers, respectively, during the Pleistocene Epoch. 

 Barrier islands and lagoons were produced during the Holocene Epoch 

 (beginning approximately 18,000 years Before Present (BP)) due to several 

 temporary stillstands during sea-level rise. Development of the modem-day 

 shoreline began approximately 3,000 to 2,500 BP. Sediment deposition from 

 major fluvial systems in the area including the Colorado River caused the 

 progradation of bayhead deltas, thereby influencing shoreline development in 

 the Matagorda Bay Area and development of the Matagorda Peninsula 

 (McGowen and Brewton 1975). 



Approximately 1,000 years ago, the Colorado River began discharging into 

 Matagorda Bay in the vicinity of present-day Matagorda, TX. Historical 

 records show that geologically, the Gulf and mainland shorelines have not 

 changed significantly in the last 140 years. 



Local changes occurring within this century have also affected the shorelines 

 of Matagorda Bay Peninsula. Historical records of surveys made in 1908 show 

 that the Colorado River channel was clogged with tangled masses of logs and 

 brush embedded with silt which restricted floodwater outflow. In 1929 the log 

 jam was removed by local conservation and reclamation districts. As a result 

 of the clearance, a substantial volume of sediment was transported into 

 Matagorda Bay, creating a delta that prograded completely across the bay. In 

 1936 local interests dredged a straight channel through the prograded delta and 

 Matagorda Peninsula that allowed the Colorado River to discharge into the Gulf 

 of Mexico (U. S. Army Engineer District, Galveston 1977). 



Human activities caused other local changes along the coastline (McGowen 

 and Brewton 1975). Construction of the Matagorda Ship Channel Jetties in 

 1965 (located approximately 40 km southwest of the Colorado River) has 

 resulted in accretion and erosion northeast and southwest of the jetties, 

 respectively. 



Chapter 2 History 



