Which geographic area of the coastal plains region contains two of Texas three largest cities

The three largest cities in Texas are the following:

Houston, largest city in the state with 2,303,000 inhabitants. San Antonio (population: 1,327, 500) Dallas (population: 1,318,000)

Both Houston and San Antonio are located in the coastal plains region in Gulf of Mexico. The Coastal Bend is the name given to the deep curved area along the Gulf.