RIO VERDE, Ariz. -- A wildfire is burning northeast of the Valley in the Tonto National Forest, near Rio Verde.The Rio Fire has burned 21 acres, according to U.S. Forest Service spokeswoman Tammy Pike.Four engines are on the ground, and several planes have made fire retardant drops. Two helicopters were also on scene.Crews will remain on the ground throughout the night."We do have retardant all the way around it," Pike said. "It is on the east side of the Verde River, and we will be keeping a few people on it overnight."No injuries have been reported, and no structures have been damaged."It's not close or threatening any because it is on the opposite side of the river of all those," Pike said.Several people who live in the area said they first spotted the smoke between 3 and 4 p.m. Wednesday."It's a little bit scary. It's so dry out here and just there's so much desert land all the way up to our houses," Megan Costolo said.The cause is under investigation.Fire restrictions have been in effect in the Tonto National Forest. Campfires, fireworks and target practice have all been banned.