San Marcos Springs, the second largest natural cluster of springs in Texas, is two miles northeast of the county courthouse in San Marcos in southeastern Hays County (at 29°53' N, 97°56' W). The springs were originally called Canocanayesatetlo (meaning "warm water," although the water is only slightly warm) by the Tonkawa Indians; they have also been known as St. Mark's Spring and recently as Aquarena Springs. The springs' artesian flow issues from the Edwards and associated limestones in three large fissures and some 200 smaller openings along the Balcones fault zone, thus forming Spring Lake and the San Marcos River. In previous centuries the springs supported a variety of wild fruits and nuts and abundant wildlife; they still support flora and fauna found nowhere else. Excavations indicate that Paleo-Indians used the springs at least 8,000 years ago, and that the Tonkawas farmed in the region 800 years ago. Early American settlers reported numerous mountain lions and bears and an occasional alligator in the vicinity. The first Europeans to see the springs were probably members of the Espinosa-Olivares-Aguirre expedition of 1709. Later in the century the headwaters of the San Marcos River were the site of a short-lived Spanish mission, San Xavier, and in the early nineteenth century the failed settlement of San Marcos de Neve was situated there. Throughout the Spanish period the springs were an important stop on the Old San Antonio Road from northern Mexico to Nacogdoches. Whites began settling in the area in 1835 and for the rest of the nineteenth century used the reliable water flow to power gins and mills. After the Civil War the springs became a stop for cattle drives up the Chisholm Trail. The construction of a large spillway at the west end of Spring Lake in the 1950s formed a popular swimming pool and led to development of an amusement park that now encompasses the springs. Between 1892 and 1978 the average flow from the springs was estimated at 4,300 liters per second. The water quality remains high, but the flow rate is reported to be increasingly threatened by well-pumping southwest of the springs.