A cheerful group of ten women — dressed in the full-skirted frocks, capri-length skirts, and sensible heels of a perfect early-1960s afternoon out — clusters on the dock at Aquarena Springs, San Marcos, Texas, as their guide gestures toward one of the park's signature glass-bottom boats preparing to depart across the gin-clear San Marcos River headwaters. Spanish moss drapes the cypress trees along the far bank, and the open hatch of the sleek white-and-red boat beckons passengers down to peer through the glass floor at the bubbling sand springs and exotic fish life below. Published by W. M. Cline Co. of Chattanooga, Tennessee (Color-King Natural Color Views series), with a color photograph by Gene Aiken, this unused chrome card captures Aquarena at the height of its mid-century popularity — a Texas attraction located on one of North America's most ecologically significant spring systems, the headwaters of the San Marcos River fed by the Edwards Aquifer.