San Marcos Springs, a major artesian outflow from the Edwards Aquifer in San Marcos, Texas, is the state’s second largest natural spring cluster and the source of most of the San Marcos River. More than 200 springs rise from fissures along the Balcones Escarpment, maintaining a constant flow and a year-round temperature of about 72 degrees Fahrenheit. The site has drawn people for millennia, with evidence of human activity reaching back roughly 11,500 years and possibly much earlier. Long important to Indigenous peoples, later settlements, trail travel, recreation, and scientific study, it is now protected as a crucial habitat for threatened species and a key focus of aquifer conservation.