Joshua Tree National Park officials have announced that the Cottonwood Visitor Center has changed its hours of operation. As of Monday, April 29, the Cottonwood Visitor Center will be open from 9 to 4 weekdays, and 8 to 4 weekends. The Oasis of Mara Visitor Center in Twentynine Palms and the Joshua Tree Visitor Center will remain open from 8 to 5.