NPS Group Campground Reservations. Reservations for group sites at Rio Grande Village, Chisos Basin, and Cottonwood campgrounds may be made year-round, up to 360 days in advance. Reservations are not accepted less than two days in advance. Group sites cannot be used without prior reservation. Reservations are not accepted less than two days in advance. Reservations are not taken between mid-April and October 31st for Rio Grande Village as it rarely fills during that time of year.