 This was observed several times during the 1800s and geological evidence suggests this regularly occurred as early as the Pleistocene period.The area was known as the "Cienega de las Ranas" ("Marsh of the Frogs") by early Spanish settlers, for the millions of tree frogs that once inhabited the forested lowlands.Lacking a direct outlet to the sea, the water table in the area was rather high and resulted in many year round artesian springs, which supported a rich variety of native plant and animal life.