Volcanic twilight over the Sonoran Desert, with ocotillo in silhouette. Fouquieria splendens. Sky color intensified by volcanic dust fired into the stratosphere by the 1991 eruption of Mount Pinatubo, one of this century's biggest volcanic explosions. Dust from this eruption had encircled our planet within three weeks, painting desert skies in heavenly pinks, purples, and an unearthly orange. Pinacate Mountains, northern Sonora, Mexico.