The Salar de Uyuni - the contiguous remnants of an ancient lake, covering more than 10,000 square kilometres in the Andes of Bolivia, South America - has now become a vast and flat white salt pan. In the rainy season, when water collects on the impervious crystalline crust of the salt pan and creates a large shallow pool, a natural mirror forms. The resulting natural mirror reflects the sky below as if it were flat - nearly perfectly; thus, space agencies use these flat/pools to test their satellite altimeters. In addition to being beautiful, this natural mirror also sits just above a large brine body containing high levels of lithium; therefore, the Salar de Uyuni marks a unique intersection of a geological phenomenon, an atmospheric event, and today's technology. The Salar's pristine surface serves as a vital calibration tool, ensuring that modern satellites accurately measure global sea levels and topographical changes.
