Brownsville, Texas, the southernmost American city on the US–Mexico border, is located on a bend of the Rio Grande, across from Matamoros, Mexico, and 20 miles from the Gulf of Mexico. The city lies in what is called the Lower Rio Grande Valley, although it’s not really a valley, but rather a delta created by movement of the river and its channels as it empties into the Gulf.
The geography and geology of the Valley, which has clayey soil that does not absorb water well, make the area prone to flooding. But as a delta region, this soil is also rich, allowing a wide variety of plants to thrive, especially around Brownsville’s resacas, or channels of water that were formed when the river would naturally overflow before it was engineered.1“Lower Rio Grande Valley: Water Management,” US Fish and Wildlife Service, Accessed November 28th, 2020. These natural features become more evident as you move outward from downtown, which is located immediately adjacent to the Rio Grande and a border crossing into Matamoros. The downtown core is a dense urban grid, which consists mainly of one- and two-story commercial buildings. The brick used for these historic buildings, most dating to the 1800s, features light yellow and russet hues, evidence of the region’s complex clay soils.
Moving away from downtown the grid changes, becoming less dense as it becomes more residential. It kinks as it intersects with resacas, highways, and the border, eventually dissolving into a suburban network of superblocks and cul de sacs.