The Basin and Range province's dynamic fault history has profoundly affected the Great Basin's water drainage system. Most precipitation in the Great Basin falls in the form of snow that melts in the spring. Rain that reaches the ground, or snow that melts, quickly evaporates in the dry desert environment. Some of the water that does not evaporate sinks into the ground to become ground water. The remaining water flows into streams and collects in short-lived lakes called playas on the valley floor and eventually evaporates. Any water that falls as rain or snow into this region does not escape out of it; not one of the streams that originate within this basin ever find an outlet to the ocean. The extent of internal drainage, the area in which surface water cannot reach the ocean, defines the geographic region called the Great Basin.