La Sal Vieja ("Old Salt") is the name given to two salt lakes six miles northwest of Raymondville in Willacy County (at 26°32' N, 97°53' W). The west lake has a surface area of 2,475 acres, and the east lake, 720 acres; they are separated by a natural isthmus. Coahuiltecan Indians are thought to have been among the first people to use salt from La Sal Vieja. In Spanish Texas these salt deposits were important items of trade between natives and the Spanish.
As late as 1920 salt was being excavated and shipped commercially from La Sal Vieja. In 1930 a skeleton, believed to be that of a Karankawa Indian who had died possibly 600 years before, was found on one of the five islands in the larger lake. A marker erected in 1936 on the old Red Gate Road nearby claims, "Here has existed since the first Spanish chronicler traversed the region a great salt lake which supplied all northern Mexico with salt." At that time Hidalgo and Willacy County Water Control and Improvement District No. 1, established in 1928, owned the water of La Sal Vieja up to the thirty-five-foot level and had the option to divert flood water to the lakes. The district first delivered water to La Sal Vieja in 1939–40; since then there has always been water in the lakes. Draining water into the lakes has been necessary only in periods of heavy rainfall, and a canal built in 1974 has made it possible to make excess water bypass La Sal Vieja. As late as 1978 La Sal Vieja was owned by eight different individuals, companies, foundations, or water-control districts in nine different tracts.
La Sal Vieja is in level to gently rolling terrain with faults and fractures, surfaced by fine sandy loam over limestone and gypsum clay; saline tolerant brush and grasses, as well as mesquite and prickly pear, grow in the area. Normal pool elevation for the west lake is fourteen to twenty-eight feet and for the east lake around twenty feet, although a maximum of ninety-four feet has been recorded. La Sal Vieja is important as a habitat for endangered and protected species and as an archeological site.