REDWOOD CITY -- A volunteer firefighter charged with setting at least five fires, including one near a San Mateo County reservoir, pleaded not guilty Wednesday to a felony arson charge, authorities said.

Nathaniel Ridgway Schmidt, 20, of Cazadero in Sonoma County, was part of the Timber Cove Volunteer Fire Department when he sparked the fire on Crystal Springs Reservoir land, District Attorney Steve Wagstaffe said. He set the flames, which burned about a quarter acre near the San Andreas Dam, "just looking for excitement," Wagstaffe said.

Schmidt also faces four felony arson charges in Sonoma County for fires he is accused of setting between July 2011 and June 2012. As a Sonoma County Sheriff's detective interviewed him about those blazes he purportedly confessed to setting all five fires.

On top of arson, Sonoma County prosecutors have also charged Schmidt with five misdemeanor counts of falsely reporting an emergency. Prosecutors allege he called authorities between January and April 2012 to report fake incidents like a car over a cliff, a swimmer and diver in distress before being caught. He's pleaded not guilty to the charges.

Defense attorneys Ross Green and Steve Gallenson didn't immediately respond to requests for comment.

Schmidt was helping with a controlled burn at Crystal Springs as part of a training exercise July 11, 2011 when the flames broke out. A supervisor told Schmidt to walk a fire line in order to make sure there were no "hot spots," but 30 minutes later he came back yelling the fire was out of control, Wagstaffe said.

Schmidt purportedly said helicopters and firefighters were needed or the flames would burn a canyon. However, crews put out the fire and investigations ruled out all causes except for someone sparking the flames.

Schmidt is out of San Mateo County Jail on $50,000 bail.

Contact Joshua Melvin at 650-348-4335. Follow him at Twitter.com/melvinreport.