San Marcos area history can be traced back almost twelve thousand years. Artifacts from Paleo-Indians, such as Clovis points, have been found in archeological excavations in Spring Lake at the headwaters of the San Marcos River. Remnants of the animals the Indians killed, such as large bison and mastodon bones, have been recovered, too. The river provided dependable fresh water as well as a good source of game.
Prior to European contact, Tonkawa Indians were the main native band in the area, with evidence of agricultural activity dating back 800 years.