Beginning about 20 million years ago, during the Miocene Epoch, both the Basin and Range and Colorado Plateau regions were uplifted as much as 3 kilometers. Great tension developed in the crust, probably related to changing plate motions far to the west. As the crust stretched, the Basin and Range Province broke up into a multitude of down-dropped valleys and elongate mountains. Yet for some reason not fully understood, the neighboring Colorado Plateau was able to preserve its structural integrity and remained a single tectonic block. Eventually, the great block of Colorado Plateau crust rose a kilometer higher than the Basin and Range.