The water in the river is mostly underground. The channel at the surface remains dry most of the time, but extreme flooding is possible. For example, during a heavy El Niño in the Mojave Desert, rains caused the Mojave River to overflow onto overpassing bridges on February 22, 1993, the most damaged being on Bear Valley Road, where Victorville and Apple Valley are separated. The water comes to the surface only in areas with impermeable rock, such as the upper and lower narrows near Victorville and in the Afton Canyon area northeast of Barstow.