Pecos Spring, a spring in West Texas northeast of Sheffield, emerged from the Edwards-Trinity aquifer and for centuries served chiefly as a vital water source in an arid landscape. Cabeza de Vaca probably passed it in 1534, Comanche used it as a campsite, and it later became a regular stop on the Old Spanish Trail and the San Antonio–El Paso Road. Near the brackish Pecos River, it provided the last good water for east-to-west travelers before a long dry stretch, making it an essential point on a major travel corridor. Its flow declined in the twentieth century and had ceased by 1961.