REEVES COUNTY, TEXAS — Travelers crossing the long stretch of arid desert spanning West Texas might stumble across an extraordinarily improbable sight — a tiny teeming wetlands, a sliver of marsh that seems like it should sit by the ocean but actually lays over 450 miles from the nearest coast.

This cienega, or desert-wetlands (an ecosystem so unusual that its name sounds like a contradiction), lies instead near a massive swimming pool and lake, all fed by clusters of freshwater springs that include the deepest underwater cave ever discovered in the U.S., stretching far under the desert's dry sands.

Famous as “the oasis of West Texas,” Balmorhea State Park now hosts over 150,000 visitors a year, drawn by the chance to swim in the cool waters of the park's crystal-blue pool, which is fed by up to 28 million gallons of water a day flowing from the San Solomon springs. The pool's steady 72 to 76 degree Fahrenheit temperatures make the waters temptingly cool in the hot Texas summer and surprisingly warm in the winter, locals say — part of the reason it's been called “the crown jewel of the desert.”